Etymology Dictionary

IDIOM,  a mode of expression peculiar to a language.  (F.,—L.,—Gk.)   'The Latin and Greeke idiom;' Milton, Of Education (R.)   Spelt idiome in Minsheu.—F. idiome, 'an ideom, or proper form of speech;' Cot.—Lat. idioma.—Gk. ἰδίωμα, an idiom, peculiarity in language.—Gk. ἰδιόω, I make my own.—Gk. ἴδιο-, crude form of  ἴδιος, one's own, peculiar to one's self.   Corrupted from the stem σϜε- with suffix -yos, as explained by Curtius, ii. 272.   'In this way (he says) from the stem σϜε-... came also σϜε-yos, σϜε-δyos, later σϜε-διos, Ϝε-διos, and finally ἴδιος.'   Cf. Skt. svayam, reflexive pronoun of the three persons, self; from the base SAWA, SWA, one's own, reflex. possess. pronoun, with suffix YA.   Der. idiom-at-ic, from ἰδίωματ-, stem of ἰδίωμα; idiom-at-ic-al, idiom-at-ic-al-ly.   Also idio-pathy, a primary disease not occasioned by another, from ἴδιο-, crude form of  ἴδιος, and παθ-, as seen in παθεῖν, to suffer (see Pathos); idio-path-ic, idio-path-ic-al-ly.   And see Idiosyncrasy.