noun (n)

• doubt about the truth of something(noun.cognition)

  Synonym:
  incredulity, mental rejection, skepticism
  

  source: wordnet30
• a rejection of belief(noun.cognition)

  Synonym:
  unbelief
  Antonym:
  belief
  

  source: wordnet30
• The act of disbelieving;; a state of the mind in which one is fully persuaded that an opinion, assertion, or doctrine is not true; refusal of assent, credit, or credence; denial of belief.(noun)

  source: webster1913