noun (n)

• an argument that is conclusive(noun.communication)

  Synonym:
  clincher, determining factor
  

  source: wordnet30
• one of a limited class of noun modifiers that determine the referents of noun phrases(noun.communication)

  Synonym:
  determinative
  

  source: wordnet30
• a determining or causal element or factor(noun.cognition)

  Synonym:
  causal factor, determinant, determinative, determining factor
  

  source: wordnet30
• One who, or that which, determines or decides.(noun)

  source: webster1913