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Yojijukugo (四字熟語): The Japanese Four-Character Idioms Explained

Yojijukugo (四字熟語) are fixed Japanese four-character idioms. They are fixed vocabulary items written in exactly four kanji, function as one semantic unit, and, in the strict sense, have a meaning that is not transparently built from the parts.12 For N2-plus learners moving past two-kanji jukugo, they are the next layer of formal Japanese vocabulary: dense, classical-flavored, and especially common in writing that wants to sound serious.3

Overview

What yojijukugo are (strict definition)

Reference works split the term in two directions. The broad sense treats any four-kanji lexeme, or dictionary word, as a 四字熟語, including transparent compound nouns such as 屋内禁煙 and 株式会社.14 The narrow / idiomatic sense, which this article tracks, limits the term to fixed four-kanji expressions whose meaning requires learned context: an origin story, a classical allusion, or a conventionalized metaphor.52

『新明解四字熟語辞典』 collects roughly 7,500 entries under this stricter idiomatic criterion. 『日本国語大辞典』 enters 四字熟語 as a sub-category of 熟語, defined as "漢字四文字で構成される熟語。多くは故事や古典に由来する慣用句" (a compound made of four kanji characters, often an idiom derived from an old story or classical text).12 The boundary with kotowaza, Japanese proverbs, is conventional rather than sharply divided: items such as 弱肉強食 and 馬耳東風 appear in both 四字熟語辞典 and ことわざ辞典 without contradiction.2

Yojijukugo and chengyu are overlapping, not identical sets

The related Chinese category is 成語 (chéngyǔ), Chinese idioms usually written in four characters. Many Japanese yojijukugo are direct chengyu loans, but not every chengyu became a yojijukugo, and not every yojijukugo has a Chinese source. English-language references gloss the term as "four-character idiom," "four-character compound," or "four-character idiomatic compound" interchangeably.4

Where yojijukugo sit inside the jukugo family

In the broadest sense, a 熟語 is any multi-kanji lexeme, or dictionary word. Two-kanji jukugo are the default form.15 Yojijukugo sit one tier above that: four-kanji units whose two halves are usually two-kanji jukugo, joined under one of a small set of classical construction patterns.6

The 漢検 study tradition catalogues four internal structural types:

PatternRelationshipWorked examples
主述 (subject + predicate)front half is subject, back half is predicate意気消沈, 本末転倒
修飾 (modifier + modified)front half modifies back half順風満帆, 一網打尽
並列 (similar meanings)two synonymous halves joined自由自在, 完全無欠
対立 (opposite meanings)two antonymous halves joined喜怒哀楽, 半信半疑

These categories are pulled from the 漢検 領域・内容 documentation.6

Register: where yojijukugo actually appear

Yojijukugo skew heavily toward formal writing. Nippon.com's editorial framing characterizes them as "compressed poetry," compact devices that carry disproportionate weight when used in writing.3 As Sino-Japanese (漢語, kango) compounds, they carry the same register weighting as 漢語 vocabulary in general: more formal than native Japanese 和語 (wago), and more native-sounding than loanwords, 外来語 (gairaigo).5

The corpus profile matches the editorial framing. High-frequency yojijukugo such as 一石二鳥, 一期一会, 試行錯誤, and 喜怒哀楽 cluster in BCCWJ (the Balanced Corpus of Contemporary Written Japanese) editorial-prose, business, and speech-text sub-corpora. They are nearly absent from casual blog and social-media sub-corpora. Per-item frequency counts are not available without a NINJAL (National Institute for Japanese Language and Linguistics) 中納言-login query, but the register skew is clear at the sub-corpus level.7

New Year's calligraphy (書き初め) and 年賀状 use yojijukugo as fixed-form auspicious wishes such as 一陽来復 and 七転八起. This is one of the few non-editorial registers where they appear at high density.2

Origins: classical Chinese, Buddhist scripture, Japanese coinage

Three historical streams account for almost every dictionary-attested yojijukugo. Sorting an unfamiliar idiom into the right stream is the fastest way to predict its register and likely meaning drift.

Classical-Chinese chengyu lineage

This is the largest single origin bucket. Yojijukugo with a directly attested classical-Chinese source draw most heavily from 『史記』, 『論語』, 『孟子』, 『荘子』, 『列子』, 『詩経』, 『礼記』, 『孫子』, and Tang and Song poetry by writers such as Li Bai, Han Yu, and Su Shi.89101112131415

A few worked examples show the range:

  • 四面楚歌: from 『史記』項羽本紀 (the Battle of 垓下, 202 BCE), where 項羽's surrounded army hears the Han forces singing Chu folk songs at night, a sign that even his homeland has surrendered.8
  • 臥薪嘗胆: semantically rooted in 『史記』越王勾踐世家 (the bile-tasting half), but the conjoined four-character form is first attested in 蘇軾's 「擬孫權答曹操書」 (11th c.).16
  • 温故知新: 『論語』為政第二・十一: 「子曰、温故而知新、可以為師矣」.9
  • 朝三暮四: the 『荘子』斉物論 and 『列子』黄帝篇 monkey-handler anecdote.11
  • 五十歩百歩: 『孟子』梁恵王上, the battlefield-retreat parable in Mencius's reply to King Hui of Liang.10
  • 切磋琢磨: 『詩経』衛風・淇奥, the praise-poem for Duke 武 of 衛, also quoted in 『論語』学而第十五.12
  • 馬耳東風: Li Bai, 「答王十二寒夜独酌有懐」.14
  • 弱肉強食: Han Yu, 「送浮屠文暢師序」.17

Most of these survive in both modern Mandarin chengyu and Japanese yojijukugo with the same kanji. But nuance, formality, or domain has often drifted over a millennium of separation. The "Good to know" section flags the practical reading hazard.4

Buddhist-scripture and religious sources

This is the second canonical origin bucket. Source texts include 『大般涅槃経』, 『阿含経』, 『仏説阿弥陀経』, 『維摩経』, 『正法念処経』, and Buddhist hagiography, or sacred biography.181920212223

  • 諸行無常: 涅槃経 偈 「諸行無常、是生滅法、生滅滅已、寂滅為楽」; popularized in Japan by the opening of 『平家物語』.1924
  • 一心不乱: 『仏説阿弥陀経』 (鳩摩羅什訳, 5th c.): 「執持名号、若一日、若二日、…若七日、一心不乱」.18
  • 四苦八苦: 『阿含経』 and 『涅槃経』, naming 生・老・病・死 plus 愛別離苦・怨憎会苦・求不得苦・五蘊盛苦.22
  • 唯我独尊: the Śākyamuni birth narrative 「天上天下唯我独尊」 in 『修行本起経』 and parallels.23
  • 言語道断: 『維摩経』阿閦仏品, originally "the path of language is severed" (the truth is beyond words); the modern Japanese reading has fully inverted to "outrageous, beyond words" in the bad sense.20
  • 自業自得: 『正法念処経』: 「自業自得果、衆生皆如是」, originally neutral karmic phrasing whose modern Japanese reading is overwhelmingly negative.21
  • 油断大敵: popular etiology traces 油断 to the 『大般涅槃経』 anecdote in which a king commands a servant to carry a bowl of oil without spilling a drop on pain of death; the four-character idiom 油断大敵 is the later Japanese moralization.19

Buddhist-sourced yojijukugo carry residual gravitas. They appear in 法話 (Buddhist sermons), 葬儀 (funerals), 年頭挨拶 (New Year's greetings), and serious editorial prose. They also tend to read more solemnly than chengyu loans of comparable frequency.3

Japanese-coined yojijukugo (和製)

Distinct from chengyu loans, 和製四字熟語 are four-character compounds in kanji form with no classical-Chinese source. They were coined in Japan from the medieval period onward.252627282930

  • 一期一会: earliest Japanese articulation in 山上宗二's 『山上宗二記』 (天正 16, 1588), recording 千利休's tea-ceremony instruction; the four-character form is canonized in 井伊直弼's 『茶湯一会集』 (安政 5, c. 1858).3132
  • 一所懸命 → 一生懸命: Kamakura-period military vocabulary for "the one domain a 御家人 was prepared to die defending." It mutated to 一生懸命 in the Edo era through phonetic confusion (一所 → 一生), with the meaning generalizing to "doing one's utmost".26
  • 我田引水: the Edo-era Japanese proverb 「我が田へ水を引く」 ("re-routing irrigation water to one's own paddy"), recast as a four-character 漢語調 compound in the Meiji era.25
  • 八方美人: a Japanese-coined Edo-period compound whose meaning shifted toward the modern pejorative "pleases everyone, commits to no one".27
  • 自画自賛: derived from the East Asian 画賛 inscription tradition. In Japan the four-character idiom takes on the metaphorical "praising one's own work" sense, not paralleled in Chinese chengyu of the same shape.33
  • 二束三文: Edo-period commerce slang from the cheap 金剛草履 priced at 二足三文. The modern spelling 二束三文 (note 束 vs. 足) is a Meiji-era and post-war re-spelling.28
  • 二人三脚: a Meiji-era school-athletics coinage tracing to the 1874 海軍兵学校寮 「競闘遊戯会」 and its subsequent 運動会 spread.29
  • 一石二鳥: a Meiji-era Japanese translation of the 17th-century English proverb "kill two birds with one stone." The Japanese form replaced earlier 「一挙両得」 as the standard rendering.30
  • 三日坊主: an Edo-era colloquial coinage for novice monks who quit within three days; no Chinese antecedent.34
  • 十人十色: an Edo-period proverbial coinage attested in the 浄瑠璃 and 洒落本 corpora.35
  • 順風満帆: a modern Japanese (Shōwa-era) crystallization. It first entered 『広辞苑』 in the 1983 third edition.36

A learner who assumes every yojijukugo "comes from China" will misread the etymological weight of a 和製 form. They may also try to use it in a Chinese-language context where it is simply not recognized.4

Onomatopoeic and proverbial intersections

Some yojijukugo overlap with kotowaza, Japanese proverbs. The boundary is conventional rather than strict.2 Items collected under ことわざ in 『故事ことわざ辞典』 and similar references include 弱肉強食, 馬耳東風, 油断大敵, and 十人十色.2 A small subset of yojijukugo are or contain 擬態語 (mimetic words) or 擬声語 (sound-symbolic words) shaped readings, such as 戦々恐々 and 喧々諤々. These are minority entries.2

The practical line for this article is simple: the corpus covered here is narrow-sense yojijukugo. These are idiomatic, non-transparent, fixed-form expressions, set against transparent four-kanji compound nouns on one side and kotowaza on the other.

Reading and structure

On'yomi dominance and exceptions

As a class of 漢語 compounds, yojijukugo are overwhelmingly read on + on + on + on, because their morphemes are Sino-Japanese.56 This default is even stronger than it is for two-kanji jukugo, because the source corpus is more uniformly classical.

Exceptions cluster in three small pockets:

  • Mixed wago and kango (重箱読み or 湯桶読み). 老若男女 (ろう-にゃく-なん-にょ) is unusual in mixing 呉音 and 漢音 readings within the same lexeme.37
  • Native or kun-mixed compounds. 一所懸命 (いっ-しょ-けん-めい) keeps a Sino-Japanese profile, but the Japanese-coined 二束三文 (に-そく-さん-もん) mixes 訓 in 束.28
  • 熟字訓-shaped idioms. These are very rare in narrow-sense yojijukugo, but possible in folk-coined four-character expressions. Learners should not expect them.

Internal structure: AB+CD, A+BCD, ABCD flowing

Beyond the four classical internal patterns catalogued above, yojijukugo also divide by how the four characters chunk:

  • AB + CD (the most common shape). Two parallel two-character jukugo joined; meaning composes from each half. Examples: 喜怒+哀楽, 半信+半疑, 切磋+琢磨, 美辞+麗句, 一刻+千金, 千差+万別, 千変+万化.6
  • A + BCD or ABC + D (subject-predicate readings). Examples: 本末+転倒, 意気+消沈, 我田+引水, 油断+大敵 (read as 「油断 (が) 大敵」).256
  • ABCD flowing (the four characters compose as a single unit). Examples: 朝三暮四, 唯我独尊, 五十歩百歩, 試行錯誤. Here the chunk does not factor cleanly into a 2+2 reading.101123

Each half of an AB + CD yojijukugo can independently show the four internal patterns (主述, 並列, 修飾, 述目). 並列 is the dominant pattern for that shape.6

Rendaku and irregular voicing inside yojijukugo

Sino-Japanese morphemes resist rendaku. Vance estimates that only about 10 percent of Sino-Japanese binoms undergo sequential voicing. The figure is even lower inside yojijukugo, because their morpheme boundaries are typically those of independent kango words.38

Lyman's Law is the dominant blocker. Where the second half of a yojijukugo already contains a voiced obstruent, rendaku is categorically blocked.3839 When rendaku does occur inside a four-character compound, the second half is almost always 和語 or has been re-lexicalized as native. Irwin documents the Sino-Japanese mononom hybrid pattern, involving single-character Sino-Japanese elements in hybrid compounds, in detail.39

Practical reading for the table below

None of the 50 entries in the top-50 list show rendaku; all halves are kango. Read each four-character item character by character in its standard on'yomi, and the table's "Reading" column will match.

Top 50 yojijukugo for N2 and N1 readers

Selection criteria

To qualify for the list, an item must meet at least two of these criteria:

  1. Dictionary-attested in 『新明解四字熟語辞典』 (Sanseido, ~7,500 entries).2
  2. Present in the 漢検 出題範囲 at 準2級 or 2 級, the standard adult-learner cutoff.406
  3. Wikipedia (ja) 「四字熟語」 article's "well-known" listing.4
  4. Editorial or newspaper attestation in BCCWJ at the sub-corpus level; no per-item count is available without a NINJAL 中納言-login query.7

The audience filter is N2-plus reading comfort. The 常用漢字 readings of all four characters must be accessible at 高校卒業 level.40 The 50 entries are grouped by origin bucket, so the table also serves as the worked-example payoff for the Origins section above.

The list (kanji, reading, literal gloss, idiomatic meaning, origin bucket)

Classical Chinese (中国古典): 20 items

四字熟語ReadingLiteral glossIdiomatic meaningSource
温故知新おんこちしん"warm the old, know the new"study the past to gain new insight『論語』為政第二9
切磋琢磨せっさたくま"cut, polish, carve, grind"mutual improvement through rivalry『詩経』衛風・淇奥12
四面楚歌しめんそか"Chu songs on all four sides"surrounded by enemies, isolated『史記』項羽本紀8
臥薪嘗胆がしんしょうたん"sleep on firewood, taste bile"endure hardship for a future goal『史記』越王勾踐世家 + 蘇軾16
朝三暮四ちょうさんぼし"three at dawn, four at dusk"fooled by superficial change『荘子』斉物論 / 『列子』黄帝篇11
五十歩百歩ごじっぽひゃっぽ"fifty paces, hundred paces"a difference of degree, not kind『孟子』梁恵王上10
馬耳東風ばじとうふう"spring breeze in a horse's ear"indifferent to advice李白「答王十二寒夜独酌有懐」14
弱肉強食じゃくにくきょうしょく"weak's flesh, strong's food"the strong prey on the weak韓愈「送浮屠文暢師序」17
一刻千金いっこくせんきん"one moment, a thousand pieces of gold"a brief moment is precious蘇軾「春夜」15
一日千秋いちじつせんしゅう / いちにちせんしゅう"one day, a thousand autumns"longing makes waiting feel endless『詩経』王風・采葛 (Japanese intensification of 一日三秋: 三秋 → 千秋)41
大同小異だいどうしょうい"great agreement, small disagreement"broadly the same with minor differences『荘子』雑篇・天下42
千変万化せんぺんばんか"a thousand shifts, ten thousand changes"constant transformation『列子』周穆王篇43
千差万別せんさばんべつ"a thousand differences, ten thousand distinctions"endless variation『景徳伝灯録』 (Northern Song)44
喜怒哀楽きどあいらく"joy, anger, sorrow, pleasure"the full range of human emotion『礼記』中庸45
風林火山ふうりんかざん"wind, forest, fire, mountain"move like wind, be still as forest, strike like fire, stand like a mountain『孫子』軍争篇 (popularized via 武田信玄's 軍旗, 1561)13
危機一髪ききいっぱつ"crisis on a single hair"a hair's-breadth from disaster韓愈「与孟尚書書」46
単刀直入たんとうちょくにゅう"single sword, direct entry"get straight to the point『景徳伝灯録』 (Northern Song)44
起死回生きしかいせい"raise the dead, return to life"dramatic recovery from a desperate situation『呂氏春秋』別類47
佳人薄命 (≒ 美人薄命)かじんはくめい / びじんはくめい"beautiful person, thin fate"the beautiful tend to die young or suffer蘇軾「薄命佳人」48
半信半疑はんしんはんぎ"half-believing, half-doubting"not fully convinced嵇康「答釋難宅無吉凶攝生論」 (3rd c.)49

Buddhist (仏教): 10 items

四字熟語ReadingLiteral glossIdiomatic meaningSource
諸行無常しょぎょうむじょう"all phenomena are impermanent"nothing lasts『大般涅槃経』 (popularized by 『平家物語』)1924
因果応報いんがおうほう"cause and effect, retribution"karmic consequences of one's deedsBuddhist canon broadly19
一心不乱いっしんふらん"one heart, no distraction"total concentration『仏説阿弥陀経』 (5th c.)18
一期一会いちごいちえ"one lifetime, one meeting"every encounter is once-in-a-lifetime千利休 / 『山上宗二記』 1588; 井伊直弼 『茶湯一会集』 c. 18583132
四苦八苦しくはっく"four sufferings, eight sufferings"overwhelming hardship『阿含経』『涅槃経』22
唯我独尊ゆいがどくそん"only I am revered"(modern) arrogant self-importance『修行本起経』 (Śākyamuni's birth declaration)23
言語道断ごんごどうだん"the path of words is severed"(modern) outrageous, unspeakable『維摩経』阿閦仏品20
自業自得じごうじとく"own karma, own gain"reaping what you sow『正法念処経』21
油断大敵ゆだんたいてき"carelessness is a great enemy"never let your guard down油断 anecdote in 『大般涅槃経』19
七転八起しちてんはっき"seven falls, eight risings"resilience, never giving upBuddhist 達磨 iconography, Edo-period 起き上がり小法師 popularization19

Japanese-coined (和製): 10 items

四字熟語ReadingLiteral glossIdiomatic meaningOrigin note
一所懸命 → 一生懸命いっしょけんめい → いっしょうけんめい"one place, life-staking" → "one life, life-staking"doing one's utmostKamakura 御家人 vocabulary, Edo phonetic shift26
我田引水がでんいんすい"draw water to one's own paddy"self-serving spinEdo proverb → Meiji four-character recasting25
八方美人はっぽうびじん"beauty for all eight directions"tries to please everyone (pejorative)Edo-period Japanese coinage27
自画自賛じがじさん"self-painting, self-praise"self-congratulationfrom the East Asian 画賛 tradition, Japanese metaphorical extension33
一石二鳥いっせきにちょう"one stone, two birds"two goals with one actMeiji-era translation of English "kill two birds with one stone"30
二束三文にそくさんもん"two bundles for three mon"dirt cheap, dumped at a lossEdo 金剛草履 pricing 二足三文; post-war re-spelling with 束28
二人三脚ににんさんきゃく"two people, three legs"working in close partnershipMeiji 1874 海軍兵学校寮 運動会 競闘遊戯会 種目 origin29
三日坊主みっかぼうず"three-day monk"a quitter, can't stick to anythingEdo-era novice-monk colloquialism34
十人十色じゅうにんといろ"ten people, ten colors"each person is differentEdo-period proverbial; 浄瑠璃 and 洒落本 attestation35
順風満帆じゅんぷうまんぱん"favorable wind, full sails"smooth sailing, going wellShōwa-era crystallization; entered 『広辞苑』 in 1983 (3rd ed.)36

General Sino-Japanese (一般): 10 items

四字熟語ReadingLiteral glossIdiomatic meaningNotes
起承転結きしょうてんけつ"rise, receive, turn, conclude"the four-part composition rubric楊載 『詩法家数』 (Yuan, c. 14th c.)50
試行錯誤しこうさくご"trial, error"trial-and-errorMeiji-era Japanese coinage translating Thorndike's "trial and error"2
用意周到よういしゅうとう"preparation, thorough"meticulous preparationcomponents from 『論語』『孟子』『史記』; conjoined form Edo-era Japanese2
適材適所てきざいてきしょ"fitting material, fitting place"the right person in the right roleEdo-era Japanese carpentry vocabulary, metaphorically extended51
急転直下きゅうてんちょっか"sudden change, straight downward"abrupt resolution, dramatic turn漢語調 Meiji-era four-character coinage2
美辞麗句びじれいく"beautiful words, ornate phrases"flowery, empty rhetoricJapanese 漢語 coinage, usually pejorative2
言行一致げんこういっち"words and deeds align"matching word with actioncomponents from 『論語』公冶長・為政; conjoined form Japanese52
不言実行ふげんじっこう"no words, actual deed"act without boastingConfucian-derived sentiment, Japanese four-character crystallization52
一心同体いっしんどうたい"one heart, same body"acting as oneclassical 漢語 compound, common in modern editorial use2
老若男女ろうにゃくなんにょ"old young male female"everyone, all ages and genders重箱読み-shaped 呉音 mix; Japanese-context lexicalization37

Where to take the list next

The 50 entries above are an index, not a study plan. The intended depth follow-up is a dedicated top-50 acquisition article under the vocabulary track, with drills, mnemonic illustrations, and register exercises. Use the table here as the entry surface, then follow into that article when it ships.

Good to know

Pitfall: treating any four-kanji string as a yojijukugo

Four-kanji compounds whose meaning is fully transparent from the parts are not idioms in the strict sense. Calling 株式会社 ("joint-stock company," composed straightforwardly from 株式 + 会社) a 四字熟語 erases the narrow-sense definition that the article rests on. 『日本国語大辞典』 and 『新明解四字熟語辞典』 both reserve the lemma for fixed expressions with non-transparent or origin-bound meaning.12 The correct framing for 株式会社 is "a four-kanji compound noun, not a yojijukugo in the narrow sense".

Pitfall: chengyu look-alikes that have drifted in Japanese

A yojijukugo and its visually identical chengyu may have moved apart over a millennium of separation in meaning, nuance, or register. 八方美人 in modern Japanese is pejorative ("a person who tries to please everyone and is therefore untrustworthy"), while the Mandarin near-equivalent 八面玲瓏 leans positive ("diplomatic, all-around competent").27 言語道断 in its 『維摩経』 source means "the path of language is severed" in the metaphysical sense that the truth is beyond words. Modern Japanese has fully inverted it to a negative "outrageous, indefensible".20 A learner who imports a Chinese-language gloss intact will misread the modern Japanese form.

Register: one per piece is striking, three per piece is pompous

Yojijukugo function as compression devices in formal Japanese. One well-placed idiom in a business email, ceremonial address, or essay closing reads as literate.3 A string of them reads as ostentatious or self-important. The "compressed poetry" framing from Nippon.com is the key observation.3 The safest registers in practice are 業務メール (business email, including お礼状 and 詫び状) and 年頭挨拶 (New Year's greetings). Casual social media and conversation are the least appropriate.7

Mnemonic: idioms that already tell their own story

Yojijukugo with vivid etymological scenes are much easier to retain than abstract Buddhist-derived items (因果応報, 諸行無常) in learner self-report. This aligns with the dual-coding principle in pedagogy. The most reliable visual scenes are:

  • 四面楚歌: picture the Battle of 垓下, surrounded, hearing your home-province's songs from the enemy camp at night.8
  • 臥薪嘗胆: picture 越王勾踐 sleeping on firewood and tasting bile every day for ten years to remember his humiliation.16
  • 一期一会: picture the tea master treating each ceremony as the only time these specific guests will ever meet.3132
  • 馬耳東風: picture a horse with the warm spring breeze hitting its ears, completely unmoved.14

Etymology: the Kanken yojijukugo strand as a de facto canon

The 日本漢字能力検定 (漢検, Japan Kanji Aptitude Test) includes a dedicated yojijukugo section starting from 3 級 ("典拠のある四字熟語の理解") and intensifies at 準2級 and 2 級 (高校卒業・大学・一般程度, 2136 字).406 For adult self-studiers, the Kanken-2 級 idiom list is the closest Japan has to an authoritative "must-know" set. The 漢検協会-published 過去問題集 effectively defines that canon at the level-claim level.40

See also

References

Footnotes

  1. 『日本国語大辞典』第二版. 小学館, 2000–2002. Entry: 四字熟語. 2 3 4 5

  2. 三省堂編修所編. 『新明解四字熟語辞典』第二版. 三省堂, 2013. 2 3 4 5 6 7 8 9 10 11 12 13 14 15

  3. Nippon.com. "The Compressed Poetry of Four-Character Idioms." https://www.nippon.com/en/nipponblog/m00111/ (register and editorial-use argument). 2 3 4 5

  4. Wikipedia (English). "Yojijukugo." https://en.wikipedia.org/wiki/Yojijukugo (broad-vs-narrow sense framing; reference-grade summary). (limitation) 2 3 4 5

  5. 『広辞苑』第七版. 岩波書店, 2018. Entries: 四字熟語, 熟語. 2 3 4

  6. 日本漢字能力検定協会.「漢検 級別問題内容 (2級・準2級・3級)」. https://www.kanken.or.jp (各級の領域・内容、特に「典拠のある四字熟語の理解」を 3 級以上で要求). 2 3 4 5 6 7 8

  7. 国立国語研究所『現代日本語書き言葉均衡コーパス』(BCCWJ). https://clrd.ninjal.ac.jp/bccwj/ (used as the corpus reference for newspaper-editorial register attestation; no per-item count available without a NINJAL 中納言-login query). 2 3

  8. 『史記』巻七 項羽本紀. 中華書局校点本, 1959. 「夜聞漢軍四面皆楚歌、項王乃大驚曰、漢皆已得楚乎、是何楚人之多也」. (Source of 四面楚歌; the four-character form is a post-classical Japanese crystallization.) 2 3 4

  9. 『論語』為政第二・第十一章. 「子曰、温故而知新、可以為師矣」. (Source of 温故知新.) 2 3

  10. 『孟子』梁恵王上. 「以五十歩笑百歩、則何如」. (Source of 五十歩百歩.) 2 3 4

  11. 『荘子』斉物論. 「狙公賦芧、曰、朝三而暮四、衆狙皆怒。曰、然則朝四而暮三、衆狙皆悦」. (Source of 朝三暮四; parallel version in 『列子』黄帝篇.) 2 3 4

  12. 『詩経』国風・衛風・淇奥. 「有匪君子、如切如磋、如琢如磨」. (Source of 切磋琢磨; the four-character collapsing happens in later commentary, including the 『論語』学而第十五 quotation of the same line.) 2 3

  13. 『孫子』軍争篇. 「其疾如風、其徐如林、侵掠如火、不動如山」. (Source of 風林火山, the popular condensation used on 武田信玄's 軍旗 from 永禄四年 (1561) per 『甲陽軍鑑』.) 2

  14. 韓愈「答王十二寒夜独酌有懐」(Tang dynasty, 9th c.). 「世人聞此皆掉頭、有如東風射馬耳」. (Source of 馬耳東風.) 2 3 4

  15. 蘇軾「春夜」(Northern Song, 11th c.). 「春宵一刻値千金」. (Source of 一刻千金.) 2

  16. 『史記』巻四十一 越王勾踐世家. 中華書局校点本, 1959. (Source of 嘗胆; the conjoined form 臥薪嘗胆 is first attested in 蘇軾「擬孫權答曹操書」, 11th c.) 2 3

  17. 韓愈「送浮屠文暢師序」(Tang dynasty, 9th c.). 「弱之肉、強之食」. (Source of 弱肉強食.) 2

  18. 『仏説阿弥陀経』(鳩摩羅什訳, 後秦, 5th c.). 「執持名号、若一日、若二日、…若七日、一心不乱」. (Source of 一心不乱.) 2 3

  19. 『大般涅槃経』. (Source of 諸行無常 偈「諸行無常、是生滅法、生滅滅已、寂滅為楽」and of the 油断 anecdote underlying 油断大敵.) 2 3 4 5 6 7

  20. 『維摩経』阿閦仏品. (Source of 言語道断 as a Buddhist metaphysical term, "the path of words is severed," before its negative semantic shift in Japanese.) 2 3 4

  21. 『正法念処経』. 「自業自得果、衆生皆如是」. (Source of 自業自得.) 2 3

  22. 『阿含経』および『大般涅槃経』. (Sources of 四苦八苦, expounding 生老病死 + 愛別離苦・怨憎会苦・求不得苦・五蘊盛苦.) 2 3

  23. 『修行本起経』(Buddhist hagiography of Śākyamuni). 「天上天下、唯我独尊」. (Source of 唯我独尊.) 2 3 4

  24. 『平家物語』巻一・祇園精舎. 「祇園精舎の鐘の声、諸行無常の響きあり」. (Japanese popularization of the Buddhist phrase 諸行無常.) 2

  25. コトバンク (出典: 『精選版 日本国語大辞典』, 小学館). Entry: 我田引水. https://kotobank.jp/word/%E6%88%91%E7%94%B0%E5%BC%95%E6%B0%B4-464765 (notes the 江戸 proverbial source 「我が田へ水を引く」 and the Meiji-era four-character crystallization). 2 3 4

  26. コトバンク (出典: 『デジタル大辞泉』, 小学館). Entry: 一所懸命. https://kotobank.jp/word/%E4%B8%80%E6%89%80%E6%87%B8%E5%91%BD-433373 (鎌倉 御家人の本領地; the Edo-era shift to 一生懸命 by phonetic confusion). 2 3

  27. コトバンク (出典: 『精選版 日本国語大辞典』, 小学館). Entry: 八方美人. https://kotobank.jp/word/%E5%85%AB%E6%96%B9%E7%BE%8E%E4%BA%BA-603022 (江戸期 用例; meaning shift toward the modern negative reading). 2 3 4

  28. コトバンク (出典: 『デジタル大辞泉』, 小学館). Entry: 二束三文. https://kotobank.jp/word/%E4%BA%8C%E6%9D%9F%E4%B8%89%E6%96%87-591886 (江戸期 金剛草履 二足三文 の俗説と用例). 2 3 4

  29. 小林肇 (三省堂辞書編集部).「【二人三脚】ににんさんきゃく」. 『ニュースを読む新四字熟語辞典』第23回. 三省堂 ことばのコラム. https://dictionary.sanseido-publ.co.jp/column/new4i23 (明治7年 (1874) 海軍兵学校寮の「競闘遊戯会」以降の運動会種目から). 2 3

  30. コトバンク (出典: 『デジタル大辞泉』, 小学館). Entry: 一石二鳥. https://kotobank.jp/word/%E4%B8%80%E7%9F%B3%E4%BA%8C%E9%B3%A5-433605 (英語 "kill two birds with one stone" の明治期日本語訳起源). 2 3

  31. 山上宗二. 『山上宗二記』. 天正十六年 (1588). 「茶湯者覚悟十躰」. 「路地ヘ入ルヨリ出ヅルマデ、一期ニ一度ノ会ノヤウニ、亭主ヲ敬ヒ畏ベシ」. (Earliest attested Japanese articulation of 一期一会; the four-character form is canonized by 井伊直弼 『茶湯一会集』 c. 1858.) 2 3

  32. 井伊直弼. 『茶湯一会集』巻頭. 安政五年 (1858) 前後成立. (Source of the modern crystallized 一期一会.) 2 3

  33. コトバンク (出典: 『デジタル大辞泉』, 小学館). Entry: 自画自賛. https://kotobank.jp/word/%E8%87%AA%E7%94%BB%E8%87%AA%E8%B3%9B-518810 (画賛 文化 由来 の和製 四字 熟語). 2

  34. コトバンク (出典: 『精選版 日本国語大辞典』, 小学館). Entry: 三日坊主. https://kotobank.jp/word/%E4%B8%89%E6%97%A5%E5%9D%8A%E4%B8%BB-636232 (出家・修行 → 還俗 の俗語起源、江戸期). 2

  35. コトバンク (出典: 『デジタル大辞泉』, 小学館). Entry: 十人十色. https://kotobank.jp/word/%E5%8D%81%E4%BA%BA%E5%8D%81%E8%89%B2-77319 (江戸期 浄瑠璃・洒落本 用例). 2

  36. 三省堂辞書編集部.「順風満帆 (じゅんぷうまんぱん)」. https://dictionary.sanseido-publ.co.jp (『広辞苑』に収録されたのは 1983 年第三版から; pre-war dictionaries do not list it; Showa-era crystallization). 2

  37. 『漢字ペディア』(日本漢字能力検定協会). Entry: 老若男女. https://www.kanjipedia.jp (mixed kun/on 重箱読み 系の頻出語例として). 2

  38. Vance, Timothy J. The Sounds of Japanese. Cambridge University Press, 2008. (Chapter on rendaku, treatment of Sino-Japanese morphemes' resistance to sequential voicing; the dictionary-based estimate that rendaku affects only ~10% of Sino-Japanese binoms.) 2

  39. Irwin, Mark. "Rendaku-Based Lexical Hierarchies in Japanese: The Behaviour of Sino-Japanese Mononoms in Hybrid Noun Compounds." Journal of East Asian Linguistics 14, 2005. http://www-h.yamagata-u.ac.jp/~irwin/site/Home_files/Irwin,%20Rendaku-Based%20Lexical%20Hierarchies%20in%20Japanese%20The%20Behaviour%20of%20Sino-Japanese%20Mononoms%20in%20Hybrid%20Noun%20compounds,%20Journal%20of%20East%20Asian%20Linguistics,%202005.pdf 2

  40. 日本漢字能力検定協会. 「各級の出題内容と審査基準」. https://www.kanken.or.jp/kanken/outline/degree.html (各級 領域・内容 における「四字熟語の理解」項目) 2 3 4

  41. 『詩経』国風・王風・采葛. 「一日不見、如三秋兮」. (Source of 一日三秋; 一日千秋 is a Japanese variant intensifying 三秋 → 千秋.)

  42. 『荘子』雑篇・天下. 「大同而与小同異、此之謂小同異」. (Source of 大同小異.)

  43. 『列子』周穆王篇. 「千変万化、不可窮極」. (Source of 千変万化.)

  44. 道原編『景徳伝灯録』 (Northern Song, 1004). Used for 単刀直入 (巻十二) and 千差万別 (巻十三). 2

  45. 『礼記』中庸. 「喜怒哀楽之未発、謂之中」. (Source of 喜怒哀楽 as a four-character unit.)

  46. 韓愈「与孟尚書書」(Tang dynasty, 9th c.). 「其危如一髪引千鈞」. (Source of 危機一髪.)

  47. 『呂氏春秋』別類篇. (Source of 起死回生; the Lu state physician anecdote.)

  48. 蘇軾「薄命佳人」(Northern Song, 11th c.). 「自古佳人多命薄、閉門春尽楊花落」. (Source of 佳人薄命 → variant 美人薄命.)

  49. 嵇康「答釋難宅無吉凶攝生論」(三国魏, 3rd c.). (Earliest attested form of 半信半疑 in the conjoined four-character pattern.)

  50. 楊載『詩法家数』 (Yuan dynasty, c. 14th c.). (Earliest extant articulation of 起承転結 / 起承轉合 as the absolute-quatrain composition rubric.)

  51. 楊雄『法言』(漢, 1st c.). (Background source for 適材適所's lexical components 「材」「所」, though the four-character form is a Japanese carpentry-vocabulary crystallization documented from the Edo period.)

  52. 『論語』公冶長第五. 「吾於人也、聴其言而観其行」. (Source of 言行一致 in the broad Confucian sense.) 2