WordNet sense 1 (the usage or vocabulary that is characteristic of a specific group of people):

accent, dialect, accent

WordNet sense 2 (an expression whose meanings cannot be inferred from the meanings of the words that make it up):

phrase, idiomatic expression, phrasal idiom, set phrase

WordNet sense 3 (a manner of speaking that is natural to native speakers of a language):

parlance

WordNet sense 4 (the style of a particular artist or school or movement):

artistic style