■ 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 ).
↘a form of expression natural to a language, person, or group.
2》 a characteristic mode of expression in music or art.
Derivatives
~atic adjective
~atically adverb
Origin
C16: from Fr. ~e , or via late L. from Gk idiōma 'private property'.