noun (n)

• the state of being certain(noun.cognition)

  Example:
  His certainty reassured the others.
  

  Antonym:
  doubt, doubtfulness, dubiety, dubiousness, incertitude, uncertainty
  

  source: wordnet30
• something that is certain(noun.attribute)

  Example:
  His victory is a certainty.
  

  Synonym:
  foregone conclusion, sure thing
  Antonym:
  precariousness, uncertainness, uncertainty
  

  source: wordnet30
• The quality, state, or condition, of being certain.(noun)

  source: webster1913