noun (n)

• a future prospect or potential(noun.cognition)

  source: wordnet30
• capability of existing or happening or being true(noun.state)

  Example:
  There is a possibility that his sense of smell has been impaired.
  

  Synonym:
  possibleness
  Antonym:
  impossibility, impossibleness
  

  source: wordnet30
• a tentative insight into the natural world; a concept that is not yet verified but that if true would explain certain facts or phenomena(noun.cognition)

  Synonym:
  hypothesis, theory
  

  source: wordnet30
• a possible alternative(noun.cognition)

  Example:
  Bankruptcy is always a possibility.
  

  Synonym:
  opening, possible action
  

  source: wordnet30
• The quality or state of being possible; the power of happening, being, or existing.(noun)

  source: webster1913