The noun idiom has 4 senses (first 3 from tagged texts)
1. (2) parlance, idiom -- (a manner of speaking that is natural to native speakers of a language)
2. (1) dialect, idiom, accent -- (the usage or vocabulary that is characteristic of a specific group of people; "the immigrants spoke an odd dialect of English"; "he has a strong German accent"; "it has been said that a language is a dialect with an army and navy")
3. (1) artistic style, idiom -- (the style of a particular artist or school or movement; "an imaginative orchestral idiom")
4. idiom, idiomatic expression, phrasal idiom, set phrase, phrase -- (an expression whose meanings cannot be inferred from the meanings of the words that make it up)