idiom

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A speech form or an expression of a given language that is peculiar to itself grammatically or cannot be understood from the individual meanings of its elements, as in keep tabs on.
2. n. The specific grammatical, syntactic, and structural character of a given language.
3. n. Regional speech or dialect.
4. n. A specialized vocabulary used by a group of people; jargon: legal idiom.
5. n. A style or manner of expression peculiar to a given people: "Also important is the uneasiness I've always felt at cutting myself off from my idiom, the American habits of speech and jest and reaction, all of them entirely different from the local variety” ( S.J. Perelman).
6. n. A style of artistic expression characteristic of a particular individual, school, period, or medium: the idiom of the French impressionists; the punk rock idiom.

Century Dictionary and Cyclopedia

1. n. A mode of expression peculiar to a language; a peculiarity of phraseology; a phrase or form of words approved by the usage of a language, whether written or spoken, and often having a signification other than its grammatical or logical one. See idiotism, 1.
2. n. The genius or peculiar cast of a language; hence, a peculiar form or variation of language; a dialect.
3. n. Synonyms Dialect, Diction, etc. See language.

Wiktionary

1. n. A manner of speaking, a way of expressing oneself.
2. n. A language or dialect.
3. n. Specifically, a particular variety of language; a restricted dialect used in a given historical period, context etc.
4. n. An artistic style (for example, in art, architecture, or music); an instance of such a style.
5. n. An expression peculiar to or characteristic of a particular language, especially when the meaning is illogical or separate from the meanings of its component words.
6. n. programming A programming construct or phraseology generally held to be the most efficient, elegant or effective means to achieve a particular result or behavior.

GNU Webster's 1913

1. n. The syntactical or structural form peculiar to any language; the genius or cast of a language.
2. n. An expression conforming or appropriate to the peculiar structural form of language.
3. n. A combination of words having a meaning peculiar to itself and not predictable as a combination of the meanings of the individual words, but sanctioned by usage; ; less commonly, a single word used in a peculiar sense.
4. n. The phrase forms peculiar to a particular author.
5. n. Dialect; a variant form of language.

WordNet 3.0

1. n. the usage or vocabulary that is characteristic of a specific group of people
2. n. the style of a particular artist or school or movement
3. n. a manner of speaking that is natural to native speakers of a language
4. n. an expression whose meanings cannot be inferred from the meanings of the words that make it up