Id"i*om (ĭd"ĭ*ŭm), n. [F. idiome, L. idioma, fr. Gr. 'idi`wma, fr. 'idioy^n to make a person's own, to make proper or peculiar; fr. 'i`dios one's own, proper, peculiar; prob. akin to the reflexive pronoun o"y^, o'i^, 'e`, and to "eo`s, 'o`s, one's own, L. suus, and to E. so.] 1. The syntactical or structural form peculiar to any language; the genius or cast of a language.

Idiom may be employed loosely and figuratively as a synonym of language or dialect, but in its proper sense it signifies the totality of the general rules of construction which characterize the syntax of a particular language and distinguish it from other tongues.
G. P. Marsh.

By idiom is meant the use of words which is peculiar to a particular language.
J. H. Newman.

He followed their language [the Latin], but did not comply with the idiom of ours.

2. An expression conforming or appropriate to the peculiar structural form of a language; in extend use, an expression sanctioned by usage, having a sense peculiar to itself and not agreeing with the logical sense of its structural form; also, the phrase forms peculiar to a particular author.

Some that with care true eloquence shall teach,
And to just idioms fix our doubtful speech.

Sometimes we identify the words with the object -- though by courtesy of idiom rather than in strict propriety of language.

Every good writer has much idiom.

It is not by means of rules that such idioms as the following are made current: "I can make nothing of it." "He treats his subject home." Dryden. "It is that within us that makes for righteousness." M. Arnold.
Gostwick (Eng. Gram.)

3. Dialect; a variant form of a language.

Syn. -- Dialect. -- Idiom, Dialect. The idioms of a language belong to its very structure; its dialects are varieties of expression ingrafted upon it in different localities or by different professions. Each county of England has some peculiarities of dialect, and so have most of the professions, while the great idioms of the language are everywhere the same. See Language.