idiom in WordNet English dictionary

1. 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"
   dialect  idiom  accent 
   
2. the style of a particular artist or school or movement
   "an imaginative orchestral idiom"
   artistic style  idiom 
   
3. an expression whose meanings cannot be inferred from the meanings of the words that make it up
   idiom  idiomatic expression  phrasal idiom  set phrase  phrase 
   
4. a manner of speaking that is natural to native speakers of a language
   parlance  idiom