Idiom
WordNet
noun
(1) The style of a particular artist or school or movement
"An imaginative orchestral idiom"
(2) A manner of speaking that is natural to native speakers of a language
(3) An expression whose meanings cannot be inferred from the meanings of the words that make it up
(4) The usage or vocabulary that is characteristic of a specific group of people
"The immigrants spoke an odd dialect of English"
"He has a strong German accent"
"It has been said that a language is a dialect with an army and navy"