An idiom is a phrase or expression that has a meaning that is not literal. Instead of using words in their usual way, idioms use them to express ideas in a special or different way. These expressions are considered formulaic language, which means their overall meaning is not the same as the meanings of the individual words used.

Idioms are found often in all languages. In English, there are about twenty-five thousand idiomatic expressions. Some well-known examples in English include "spill the beans" (which means "to reveal secret information"), "it's raining cats and dogs" (which means "it is raining heavily"), and "break a leg" (which means "to wish someone good luck").

Derivations

Many common sayings were originally used in a literal way, but sometimes their meanings changed over time, leading to new stories about where the phrase came from—often called folk etymology. For example, the phrase "spill the beans" (which means to reveal a secret) was first recorded in 1919. It is said to come from an ancient method of voting, where people placed beans in jars, and if the beans were spilled, the results could be seen too early.

Other sayings are intentionally not literal. For instance, "break a leg" is a phrase used to wish someone good luck before a performance or presentation. Even though it sounds like it means something harmful, it is meant to be encouraging.

Compositionality

In linguistics, idioms are often seen as phrases that do not follow the idea of compositionality. Compositionality is a key concept when studying idioms. This idea suggests that the meaning of a whole phrase should be understood by combining the meanings of each individual word in the phrase. If someone knows the meaning of each word, they should be able to understand the whole phrase.

For example, the phrase "Fred kicked the bucket" can be understood in two ways. If taken literally, it means Fred physically kicked a bucket. However, the idiomatic meaning is different: it means Fred has died. Most people do not naturally connect the literal meaning to the idiomatic one. This shows that the idiomatic meaning is stored as a single unit, separate from the literal meaning.

In phraseology, idioms are described as a type of phraseme, where the meaning is not simply the sum of the meanings of the individual words. John Saeed explains that idioms form when words are used together so often that they become fixed phrases. These fixed phrases change the usual meanings of the individual words and create a new expression. Idioms are often difficult to translate because translating them word-for-word can change their meaning or make them unclear in another language.

When two or three words are used together in a specific order repeatedly, they form an irreversible binomial. For example, the phrase "left high and dry" is a fixed expression, but "left dry and high" is not used. Not all irreversible binomials are idioms. For instance, "chips and dip" is a fixed phrase, but its meaning is clearly based on the meanings of the individual words.

Mobility

Idioms can be used in different ways. Some idioms are used only in a standard form, while others can be changed in sentence structure, such as by rearranging parts of the sentence or using different grammatical forms. These changes show that the parts of the idiom can be separated. Idioms that allow such changes keep their usual meaning, while those that do not change keep their fixed form.

Some idioms are not made up of parts that have separate meanings. For example, "kick the bucket" means "to die," and the words "kick" and "bucket" do not have their usual meanings in this case. In contrast, idioms like "spill the beans," which means "to reveal a secret," use parts that have their own meanings: "spill" suggests sharing something, and "beans" represents a secret. These idioms have a similar structure between their surface form and their actual meaning.

The ability to change an idiom also depends on how closely its literal meaning connects to its idiomatic meaning. This connection is called motivation or transparency. Idioms that are not made up of separate parts usually cannot be changed by adding words like adjectives. However, idioms that are motivated can have their words replaced with similar ones. For example, "oil the wheels" and "grease the wheels" both use similar literal meanings for "oil" and "grease." These changes are only possible when the literal and idiomatic meanings are clearly related. For example, "kick the bucket" cannot become "kick the pot" because the literal meaning of "bucket" is not related to the idiom's meaning.

In dependency grammar, idioms are treated as a group of words that must stay together and cannot be interrupted by other words. Even though changes in sentence structure can disrupt the idiom's usual form, this rule only applies when the idiom is treated as a single unit in a dictionary.

Some idioms can be changed in many ways and are considered metaphors. For example, "jump on the bandwagon," "pull strings," and "draw the line" use parts that have their own meanings. In "jump on the bandwagon," "jump on" means to join something, and "bandwagon" refers to a group or cause. These idioms are made up of parts that can be understood individually.

Translation

A word-by-word translation of an unclear idiom may not give the same meaning in other languages. The English idiom "kick the bucket" has similar expressions in other languages, such as "kopnąć w kalendarz" ("kick the calendar") in Polish, "casser sa pipe" ("to break one’s pipe") in French, and "tirare le cuoia" ("pulling the leathers") in Italian.

Some idioms are clear. Their meaning can be understood if they are translated literally. For example, "lay one's cards on the table" means to reveal hidden intentions or a secret. Transparency depends on how much the meaning changes. Idioms like "spill the beans" (to reveal a secret) and "leave no stone unturned" (to try everything to achieve a goal) are mostly literal but use slight metaphors. Another type of idiom includes words that have multiple meanings, depending on the context. This is common in English, where words can refer to an action, the people who do it, the object used, the place or time of the action, or even a verb.

Idioms can be confusing for people who do not know them. Students learning a new language must learn idiomatic phrases as part of their vocabulary. Many common words in languages have origins in idioms but lose their figurative meanings over time. For example, in Portuguese, the phrase "saber de coração" ("to know by heart") was shortened to "saber de cor" and later became the verb "decorar," which means "to memorize."

In 2015, TED collected 40 unusual idioms that cannot be translated directly. One example is the Swedish phrase "to slide in on a shrimp sandwich," which describes people who reached a position without working for it.

Some idioms are shared across languages. For example, the Arabic phrase "في نفس المركب" ("in the same boat") has the same figurative meaning as the English idiom "in the same boat." Another example is the Japanese phrase "一石二鳥" ("isseki ni chō"), which translates to "one stone, two birds," similar to the English phrase "to kill two birds with one stone."

According to German linguist Elizabeth Piirainen, the idiom "to get on one's nerves" has the same figurative meaning in 57 European languages. She also notes that the phrase "to shed crocodile tears," which means to show fake sadness, is used in many languages, including Arabic, Swahili, Persian, Chinese, Vietnamese, Mongolian, and others.

The origins of idioms that appear in multiple languages are unclear. One idea is that these idioms come from language contact, such as when people translate phrases word for word (called a calque). Piirainen suggests this can happen through the use of a common language, like a lingua franca, where speakers learn expressions from other languages. Other theories suggest these idioms may come from a shared ancestor language or from humans naturally using similar metaphors.

Non-compositionality

The meaning of idioms is not always clear from the words they contain, which makes it hard for some theories about sentence structure to explain them. Many idioms have fixed words that do not act as parts of a sentence in any way. For example:

How do we get to the bottom of this situation?

The fixed words in this idiom (highlighted) are not considered a single part of the sentence in any theory's analysis. This is because the object of the preposition (here, "this situation") is not part of the idiom but instead is a separate part of the sentence. This can be seen because "this situation" can change, such as in: How do we get to the bottom of this situation / the claim / the phenomenon / her statement / etc. This shows that theories of sentence structure that rely on parts of sentences as the main unit are challenged. It is still unclear how meaning is connected to sentence structure. This issue has led to much discussion in linguistics and is a key reason for the development of the Construction Grammar framework.

A newer approach to analyzing idioms in sentence structure moves away from focusing on parts of sentences and instead uses a unit called a "catena." The term "catena" was introduced by William O'Grady in 1998. A catena is any word or group of words that are connected through relationships. The fixed words in idioms are stored as catenae in the language's dictionary, making them concrete units of sentence structure. Examples from sentence diagrams show this:

The fixed words of the idiom (highlighted) in each example are connected through relationships and form a catena. The parts of the sentence outside the idiom (written normally) are not part of the idiom. Two examples of proverbs are shown:

The fixed words of the proverbs (highlighted) again form a catena each time. Words like "nitty-gritty" and "always" are not part of the proverbs and do not interrupt the fixed words. A note about the catena-based analysis is that idioms are stored as catenae in the dictionary. However, in actual sentences, some idioms can be separated by other types of sentence structures.

The catena-based analysis helps explain how meaning is built from parts. The Principle of Compositionality can still be followed. Meaning is connected to catenae, many of which are not parts of sentences.

Studies have explored ways to help children with different conditions, such as autism, moderate learning difficulties, developmental language disorder, and typically developing weak readers, understand idioms.