Phraseme

A phraseme, also called a set of thoughts, set phrase, idiomatic phrase, multi-word expression (in computational linguistics), or idiom, is a multi-word or multi-morphemic utterance at least one of whose components is selectionally constrained or restricted by linguistic convention such that it is not freely chosen. In the most extreme cases, there are expressions such as X kicks the bucket ≈ ‘person X dies of natural causes, the speaker being flippant about X’s demise’ where the unit is selected as a whole to express a meaning that bears little or no relation to the meanings of its parts. All of the words in this expression are chosen restrictedly, as part of a chunk. At the other extreme, there are collocations such as stark naked, hearty laugh, or infinite patience where one of the words is chosen freely (naked, laugh, and patience, respectively) based on the meaning the speaker wishes to express while the choice of the other (intensifying) word (stark, hearty, infinite) is constrained by the conventions of the English language (hence, *hearty naked, *infinite laugh, *stark patience). Both kinds of expression are phrasemes, and can be contrasted with ’’free phrases’’, expressions where all of the members (barring grammatical elements whose choice is forced by the morphosyntax of the language) are chosen freely, based exclusively on their meaning and the message that the speaker wishes to communicate.

Phrasemes can be broken down into groups based on their compositionality (whether or not the meaning they express is the sum of the meaning of their parts) and the type of selectional restrictions that are placed on their non-freely chosen members. Non-compositional phrasemes are what are commonly known as idioms, while compositional phrasemes can be further divided into collocations, clichés, and pragmatemes.

A phraseme is an idiom if its meaning is not the predictable sum of the meanings of its component—that is, if it is non-compositional. Generally speaking, idioms will not be intelligible to people hearing them for the first time without having learned them. Consider the following examples (an idiom is indicated by elevated half-brackets: ˹ … ˺):

In none of these cases are the meanings of any of the component parts of the idiom included in the meaning of the expression as a whole.

...
Wikipedia