Definition:
"A form of expression, construction or phrase peculiar to a language and often possessing a meaning other than its grammatical or logical one."
Cuddon, J. A. A Dictionary of Literary Terms. 3rd ed., Oxford, Blackwell
Reference, 1991.
Informal Definition:
A pairing of words that bears a meaning or sense different from that of the words individually.
Etymology:
From French idiome and Late Latin idioma "a peculiarity in language," and from the Greek idioma, meaning roughly "a manifestation of the peculiar." It is also related to the Greek idioumai "to appropriate oneself" and idios "particular to oneself." The word idiom emerged in the late 16th century, and the above meanings combine to convey a sense of linguistic peculiarity or singularity.
Harper, Douglas. "idiom." Online Etymology Dictionary, www.etymonline.com/
search?q=idiom. Accessed 29 Aug. 2022.
Purpose:
Idioms are used both in written literature and common speech. They serve several main purposes: conveying a meaning or sense in a small number of words, setting or supporting a tone, and as euphemisms.
Idioms are often commonly used and understood by speakers of a language, and as such they can be used to communicate more efficiently. For example, a student talking about a late assignment might say, "It's better to have completed it after the deadline than not at all." However, for efficiency, they might instead use a common idiom, "better late than never." In this situation, by using an idiom, the speaker communicates the same thing using considerably less words. Therefore, idioms can be used as a means of efficient communication.
Additionally, an idiom can be used to fortify a tone in speech or written text. For example, someone might use the idiom, "It's raining cats and dogs" instead of "It's raining very hard." The use of this idiom most often establishes a light tone, drawing humor from a situation that might otherwise be seen as inconvenient. Additionally, the idiom here serves to exaggerate the truth, as the statement within it is impossible: cats and dogs cannot rain from the sky. Such exaggeration can establish a tone of absurdity.
Sometimes, an idiom might be used as a euphemism, or a word or phrase that softens the impact of a piece of speech. For example, someone delivering news of a loved one's passing might say, "He saw the light" instead of "He died." Seeing a light is commonly held to be a shared experience of people who are dying. The use of this idiom reduces the emotional impact of the news. Therefore, idioms can be used as euphemisms.
Benjamin McNeill