noun (n)

• a basis for comparison; a reference point against which other things can be evaluated(noun.communication)

  Synonym:
  measure, standard, touchstone
  

  source: wordnet30
• the ideal in terms of which something can be judged(noun.cognition)

  Synonym:
  standard
  

  source: wordnet30
• A standard of judging; any approved or established rule or test, by which facts, principles opinions, and conduct are tried in forming a correct judgment respecting them.(noun)

  source: webster1913