Learn how to say Idiom correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word idiom:
1a 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.
2a characteristic mode of expression in music or art:
they were both working in a neo-Impressionist idiom
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’