noun (n)

• the state of being unsure of something(noun.cognition)

  Synonym:
  doubt, dubiety, dubiousness, incertitude, uncertainty
  Antonym:
  certainty
  

  source: wordnet30
• uncertainty about the truth or factuality or existence of something(noun.attribute)

  Synonym:
  doubt, dubiousness, question
  

  source: wordnet30
• State of being doubtful.(noun)

  source: webster1913