Chengyu (traditional Chinese: 成語; simplified Chinese: 成语; pinyin: chéngyǔ; trans. "set phrase") are a type of traditional Chinese idiomatic expressions, most of which consist of four Chinese characters. Chengyu were widely used in Literary Chinese and are still common in written vernacular Chinese writing and in the spoken language today. According to the most stringent definition, there are about 5,000 chengyu in the Chinese language, though some dictionaries list over 20,000. Chengyu are considered the collected wisdom of the Chinese culture, and contain the experiences, moral concepts, and admonishments from previous generations of Chinese speakers. Chengyu still play an important role in Chinese conversation and education.^[1][2] Chinese idioms are one of four types of formulaic expressions (熟语; 熟語; shúyǔ), which also include collocations (惯用语; 慣用語; guànyòngyǔ), two-part allegorical sayings called xiehouyu, and proverbs (谚语; 諺語; yànyǔ).

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While not the only idioms in Chinese, they are often referred to as Chinese idioms or four-character idioms.

Chengyu are mostly derived from ancient literature, including the pre-Qin classics, poetry from all periods of Chinese history, and late imperial vernacular novels and short stories. A small number were constructed in the 19th and early 20th centuries from Western source materials. Among the early classical literature, the lyrical imagery from the Classic of Poetry, and the detailed stories recorded in the Zuo Zhuan and the Records of the Grand Historian serve as particularly rich source materials for chengyu. Since the Shijing poems consist of four-character lines, some chengyu are direct quotes from the Classic of Poetry. For example, 萬夀無疆 'ten-thousand year lifespan without bound', a traditional expression to wish someone a long life that often appears on bowls and tableware, quotes the poem "Tian Bao" (天保, poem #166) in the Lesser Court Hymns section of the Classic of Poetry. More commonly, however, chengyu are created by succinctly paraphrasing or summarizing the original text, usually by selecting the most salient characters from the passage in question and inserting any necessary classical grammatical particles.

As such, chengyu are fossilized expressions that use the vocabulary and follow the syntactic rules of Literary Chinese. Consequently, they convey information more compactly than normal vernacular speech or writing. They may contain subject and predicate and act as an independent clause (or even twin two-character independent clauses in parallel), or they may play the role of any part of speech in a sentence, acting syntactically as an adjective, adverb, verb, or noun phrase. In both speech and writing, they serve to succinctly convey a complex or multifaceted situation, scene, or concept, and used fittingly and elegantly, they also mark a speaker or writer's erudition.

The meaning of a chengyu usually surpasses the sum of the meanings carried by the four characters, as chengyu are generally meant to convey the message or moral of the myth, story or historical event from which they were derived. Thus, even after translation into modern words and syntax, chengyu in isolation are often unintelligible without additional explanation. Since they often contain a classical allusion, known as a diǎngù (典故), elementary and secondary school students in greater China learn chengyu as part of the classical curriculum in order to study the context from which the chengyu was born.

Often the four characters reflect the moral behind the story rather than the story itself. For example, the phrase "破釜沉舟" (pò fǔ chén zhōu^ⓘ, lit: "break the pots and sink the ships") is based on a historical account where the general Xiang Yu ordered his troops to destroy all cooking utensils and boats after crossing a river into the enemy's territory. He won the battle because of this "no-retreat" strategy. Thus, the idiom is used as a verb phrase with the meaning "to make an all-out effort to achieve success by the deliberate removal of recourse or backup." Similar phrases are known in the West, such as "Burning one's boats", "burning one's bridges", "Point of no return" or "Crossing the Rubicon".

Another example is 瓜田李下 (guātián lǐxià^ⓘ 'melon field, beneath the plums', whose meaning relates to the appearance of misconduct or impropriety. It is derived from an excerpt of a Han-era poem (樂府詩《君子行》, Yuèfǔ Shī "Jūnzǐ Xíng"). The poem includes the lines 'don't adjust your shoes in a melon field, and don't tidy your hat under the plum trees' (瓜田不納履，李下不整冠, guā tián bù nà lǚ, lǐ xià bù zhěng guān^ⓘ), admonishing the reader to avoid situations where, however innocent, he might be suspected of doing wrong. The idiom is impossible to understand without the background knowledge of the origin of the phrase.

Some idioms have had their literal meanings overtake their original ones. For example, 'wind from an empty cave' (空穴來風, kōng xué lái fēng), despite now being used to describe rumors without source, originally referred to rumors with actual, solid sources or reasons. Likewise, 'bare-faced facing the emperor' (素面朝天 is now used to describe beauty that does not require make-up, e.g., when entering court, while its original meaning was "to be confident in one's true look".

However, not all chengyu have stories to draw morals from. An example is 言而無信 'speaking, yet without trust', referring to one who cannot be trusted despite what he says, an essentially deceitful person. It is generally acknowledged as a chengyu as it comes from the Analects. The idiom is succinct in its original meaning and would likely be intelligible to anyone learned in formal written Chinese, though yán (言) is no longer commonly used as a verb.

There are a few chengyu that are not four characters in length. An example is the seven-character 醉翁之意不在酒 'The Old Drunkard's attention is not directed towards his wine'. This is a direct quote from Ouyang Xiu's essay An Account of Old Drunkard's Pavilion (醉翁亭記), in which the author, as the Old Drunkard, expresses his true intention of enjoying the scenery of the mountains and rivers as he drinks. As an idiom, it expresses the situation where one does something with an ulterior though benign motive in mind.

Some chengyu have English equivalents. For example, 言不由衷 'speak not from the bosom' and 'to speak with one's tongue in one's cheek' share idiomatic meanings. The Chinese not having conducted maritime explorations of the North Atlantic during imperial times, the expression 冰山一角 'one corner of an ice mountain' is a rare example of a chengyu that emerged in the early 20th century after contact with the West as a translation of the expression "tip of the iceberg," thus sharing both their literal and idiomatic meanings.^[3] Another expression 火中取栗 'extracting chestnuts from the fire', originating from a La Fontaine fable, means "to be duped into taking risks for someone else," used in much the same way as the expression "cat's paw" in English is another example of an "international" chengyu. Though they are recent in origin, they are constructed using the vocabulary and syntax of Literary Chinese and fits within the four-character scheme, making them chengyu.

Chinese idioms can also serve as a guide through Chinese culture. Chengyu teach about motifs that were previously common in Chinese literature and culture. For example, idioms with nature motifs – e.g., mountains, water, and the Moon – are numerous. Works considered masterpieces of Chinese literature – such as the Four Great Classical Novels^[4] – serve as the source for many idioms, which in turn condense and retell the story.

All Chinese people know idioms, though the total number known by any one individual will depend on their background. Idioms are such an important part of Chinese popular culture that there is a game called 成語接龍 'connect the chengyu' that involves someone calling out an idiom, with someone else then being supposed to think of another idiom to link up with the first one, so that the last character of the first idiom is the same as the first character of the second idiom, and so forth.

The following three examples show that the meaning of the idiom can be totally different by only changing one character.

• 一(yí) 日(rì) 千(qiān) 秋(qiū) : "One day, a thousand autumns."
  • Meaning: implies rapid changes; one day equals a thousand years
• 一(yí) 日(rì) 千(qiān) 里(lǐ) : "One day, a thousand miles."
  • Meaning: implies rapid progress; traveling a thousand miles in a day
• 一(yí) 日(rì) 三(sān) 秋(qiū) : "One day, three autumns."
  • Meaning: greatly missing someone; one day feels as long as three years

• Four Gentlemen
• Four Treasures of the Study
• Three Friends of Winter
• Crouching Tiger, Hidden Dragon
• Seek truth from facts
• When two tigers fight
• Mirror Flower, Water Moon

Yojijukugo is the similar format in Japanese. The term yojijukugo (四字熟語, four character idiom) is autological. Many of these idioms were adopted from their Chinese counterparts and have the same or similar meaning as in Chinese. The term koji seigo (故事成語, historical idiom) refers to an idiom that comes from a specific text as the source. As such, the overwhelming majority of koji seigo comes from accounts of history written in classical Chinese. Although a great many of the Japanese four-character idioms are derived from the Chinese, many others are purely Japanese in origin. Some examples:

• 花鳥風月 ka, chō, fū, getsu ("Flower, Bird, Wind, Moon"; beauties of nature)
• 一期一会 ichigo ichie (once-in-a-lifetime experience)
• 傍目八目 okamehachimoku (a bystander's vantage point)
• 手前味噌 temaemiso (singing one's own praises; tooting one's own horn)
• 二股膏薬 futamatagōyaku (double-dealer; time-server)
• 風林火山 fū, rin, ka, zan ("wind, woods, fire, mountain"; military proverb coming from Sun Tzu's "Art of War"; see also Fūrinkazan)

The Korean equivalent are Sajaseong-eo (사자성어; Hanja: 四字成語).^[5] They have similar categorization to Japanese ones, such as Gosaseong-eo (고사성어; Hanja: 故事成語) for historical idioms.^[6]

Four word idioms or any idiom in Vietnamese are known as thành ngữ (chữ Hán: 成語, literally "set phrase/speech"). A large amount of idioms originating from Classical Chinese have been borrowed into the language, but there exists native counterparts to the Classical Chinese idioms. There are also many idioms that are Vietnamese in origin. Vietnamese idioms can be classified into Sino-Vietnamese idioms (Vietnamese: thành ngữ Hán Việt, chữ Hán Nôm: 成語漢越) and native Vietnamese idioms (Vietnamese: thành ngữ thuần Việt, chữ Hán Nôm: 成語純越) that were once written in chữ Nôm, are now written in the Latin-based Vietnamese alphabet.

• Idiom
• Chinese characters
• Xiehouyu, typically longer Chinese proverbs
• Homophonic puns in Mandarin Chinese
• Proverbs commonly said to be Chinese
• Mulberry fields (idiom)

• Herbert Allen Giles (1873). A dictionary of colloquial idioms in the Mandarin dialect. SHANGHAI: A.H. de Carvalho. pp. 65. Retrieved 10 February 2012.(Harvard University)(Digitized Jul 22, 2005)
• Herbert Allen Giles (1873). A dictionary of colloquial idioms in the Mandarin dialect. SHANGHAI: A.H. De Carvalho. pp. 65. Retrieved 10 February 2012.(Harvard University)(Digitized Mar 4, 2009)
• Jiao, Liwei; Kubler, Cornelius C.; Zhang, Weiguo (2013). 500 Common Chinese Idioms: An Annotated Frequency Dictionary (Kindle ed.). Oxon, UK: Routledge.
• Pan, Weigui (2000). A Chinese-English Dictionary of Chinese Idioms. Beijing: Sinolingua.