The first meaning, idiom, is a style or a form of artistic expression that is characteristic of an individual, a period or movement, or a medium or instrument. And the second explication is an expression in the usage of a language that is peculiar to itself either in having a meaning that cannot be derived from the conjoined meanings of its elements (such as “up in the air”) or in its grammatically atypical use of words (such as “give way”).