Idiom
Part of speech: noun
Definition: A manner of speaking, a way of expressing oneself. An artistic style (for example, in art, architecture, or music); an instance of such a style. A locution peculiar of a particular language, that cannot be understood by way of a literal translation. A communicative system under study, which could be called either a dialect or a language, when its status as a language or dialect is irrelevant. A programming technique which experienced programmers in a language are assumed to know.
Metaphor
Part of speech: noun
Definition: The use of a word or phrase to refer to something that it isn't, invoking a direct similarity between the word or phrase used and the thing described, but in the case of English without the words like or as, which would imply a simile.The word or phrase used in this way. An implied comparison.