Word Origin & History
idiom1588, "form of speech peculiar to a people or place," from M.Fr. idiome, from L.L. idioma "a peculiarity in language," from Gk. idioma "peculiarity, peculiar phraseology," from idioumai "I make my own," from idios "personal, private," prop. particular to oneself, from PIE *swed-yo-, suffixed form of
base *s(w)e-, pronoun of the third person and reflexive (referring back to the subject of a sentence), also used in forms denoting the speaker's social group, "(we our-)selves" (cf. Skt. svah, Avestan hva-, O.Pers. huva "one's own," khva-data "lord," lit. "created from oneself;" Gk. hos "he, she, it;" L. suescere "to accustom, get accustomed," sodalis "companion;" O.C.S. svoji "his, her, its," svojaku "relative, kinsman;" Goth. swes "one's own;" O.N. sik "oneself;" Ger. Sein; O.Ir. fein "self, himself"). Idiomatic is first attested 1712.