1.  idiom(n = noun.communication) parlance - a manner of speaking that is natural to native speakers of a language;
is a kind of expression, formulation
Derived forms adjective idiomatic₁, adjective idiomatical₁

2.  idiom(n = noun.communication) accent, dialect - 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"
is a kind of non-standard speech
has particulars: eye dialect, patois

3.  idiom(n = noun.attribute) artistic style - the style of a particular artist or school or movement; "an imaginative orchestral idiom"
is a kind of fashion, manner, mode, style, way
has particulars: baroque, baroqueness, classical style, order, rococo, high renaissance, treatment, neoclassicism, classicalism, classicism, romantic movement, romanticism

4.  idiom(n = noun.communication) idiomatic expression, phrasal idiom, phrase, set phrase - an expression whose meanings cannot be inferred from the meanings of the words that make it up;
is a kind of expression, locution, saying
has particulars: ruralism, rusticism
Derived form adjective idiomatic₁

1.  The syntactical or structural form peculiar to any language; the genius or cast of a language. [1913 Webster]
"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." [1913 Webster]
"By idiom is meant the use of words which is peculiar to a particular language." [1913 Webster]
"He followed their language [the Latin], but did not comply with the idiom of ours." [1913 Webster]

2.  An expression conforming or appropriate to the peculiar structural form of a language. [1913 Webster]
"Some that with care true eloquence shall teach,
And to just idioms fix our doubtful speech." [1913 Webster]

3.  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; as, an idiomatic expression; less commonly, a single word used in a peculiar sense. [1913 Webster]
"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." [1913 Webster]
"Sometimes we identify the words with the object -- though by courtesy of idiom rather than in strict propriety of language." [1913 Webster]

4.  The phrase forms peculiar to a particular author; as, written in his own idiom. [1913 Webster]
"Every good writer has much idiom." [1913 Webster]

5.  Dialect; a variant form of a language. [1913 Webster]

idiom, n.
1 a group of words established by usage and having a meaning not deducible from those of the individual words (as in over the moon, see the light).
2 a form of expression peculiar to a language, person, or group of people.
3 a the language of a people or country. b the specific character of this.
4 a characteristic mode of expression in music, art, etc.

Etymology:
F idiome or LL idioma f. Gk idioma -matos private property f. idios own, private

N  neology, neologism, newfangled expression, nonce expression, back-formation, caconym, barbarism, archaism, black letter, monkish Latin, corruption, missaying, malapropism, antiphrasis, pun, paranomasia, play upon words, word play, double- entendre, palindrome, paragram, anagram, clinch, abuse of language, abuse of terms, dialect, brogue, idiom, accent, patois, provincialism, regionalism, localism, broken English, lingua franca, Anglicism, Briticism, Gallicism, Scotticism, Hibernicism, Americanism, Gypsy lingo, Romany, pidgin, pidgin English, pigeon English, Volapuk, Chinook, Esperanto, Hindustani, kitchen Kaffir, dog Latin, macaronics, gibberish, confusion of tongues, Babel, babu English, chi-chi, figure of speech, byword, colloquialism, informal speech, informal language, substandard language, vernacular, vulgar language, obscene language, obscenity, vulgarity, jargon, technical terms, technicality, lingo, slang, cant, argot, St. Gile's Greek, thieves' Latin, peddler's French, flash tongue, Billingsgate, Wall Street slang, pseudology, pseudonym, Mr, So-and-so, wha d'ye call 'em, whatchacallim, what's his name, thingummy, thingumbob, je ne sais quoi, neologist, coiner of words, neologic, neological, archaic, obsolete, colloquial, Anglice.

N  phrase, expression, set phrase, sentence, paragraph, figure of speech, idiom, idiotism, turn of expression, style, paraphrase, periphrase, motto, phraseology, expressed, idiomatic, in round terms, in set terms, in good set terms, set terms, in set phrases.

idiom neutral, phrasal idiom