▸ noun
1 a group of words established by usage as having a meaning not deducible from those of the individual words (e.g. over the moon, see the light).
▪ [mass noun] a form of expression natural to a language, person, or group of people:
he had a feeling for phrase and idiom.
▪ the dialect of a people or part of a country.
– ORIGIN late 16th century: from French idiome, or via late Latin from Greek idiōma ‘private property, peculiar phraseology’, from idiousthai ‘make one's own’, from idios ‘own, private’.