ETYM French idiome, Latin idioma, from Greek idioma, from idioyn to make a person's own, to make proper or peculiar.
An expression whose meanings cannot be inferred from the meanings of the words that make it up; SYN. idiomatic expression, phrasal idiom, set phrase, phrase.
Language or dialect peculiar to a people, region, class, etc.; linguistic expression peculiar to itself in form, grammar, etc.; style of artistic expression characteristic of a person, period, medium etc.
Any expression that is peculiar to a language and cannot be translated or interpreted literally.