noun (n)

• a manner of speaking that is natural to native speakers of a language(noun.communication)

  Synonym:
  parlance
  

  source: wordnet30
• the usage or vocabulary that is characteristic of a specific group of people(noun.communication)

  Synonym:
  accent, dialect
  

  source: wordnet30
• the style of a particular artist or school or movement(noun.attribute)

  Example:
  An imaginative orchestral idiom.
  

  Synonym:
  artistic style
  

  source: wordnet30
• an expression whose meanings cannot be inferred from the meanings of the words that make it up(noun.communication)

  Synonym:
  idiomatic expression, phrasal idiom, phrase, set phrase
  

  source: wordnet30
• The syntactical or structural form peculiar to any language; the genius or cast of a language.(noun)

  source: webster1913