An idiom is an expression whose meaning is not compositional?that is, whose meaning does not follow from the meaning of the individual words of which it is composed. For example, the English phrase to kick the bucket means to die. A listener knowing the meaning of kick and bucket will not thereby be able to predict that the expression can mean to die. Idioms are often, though perhaps not universally, classified as figures of speech.
Idioms typically admit two different interpretations: a literal one and a nonliteral (or figurative) one. Continuing with the previous example, the phrase to kick the bucket can, in fact, refer to the act of giving a kick to a bucket, but this interpretation is usually not the intended one when a native speaker uses the phrase. This aspect of idioms can be frustrating for students of a new language.
Idioms are often colloquial metaphors. The most common ones can have deep roots, traceable across many languages. Many have translations in other languages, some of which are direct. For example, get lost! ? which means go away or stop bothering me?is said to be a direct translation or calque from an older Yiddish idiom.
While many idioms are clearly based in conceptual metaphors such as "time as a substance", "time as a path", "love as war" or "up is more", the idioms themselves are often not particularly essential, even when the metaphors themselves are. For example "spend time", "battle of the sexes", and "back in the day" are idiomatic and based in essential metaphors, but one can communicate perfectly well without them. In forms like "profits are up", the metaphor is carried by "up" itself. The phrase "profits are up" is not itself an idiom. Practically anything measurable can be used in place of "profits": "crime is up", "satisfaction is up", "complaints are up" etc. Truly essential idioms generally involve prepositions, for example "out of" or "turn into".
