noun (n)

• an event that might have been arranged although it was really accidental(noun.event)

  Synonym:
  happenstance
  

  source: wordnet30
• the quality of occupying the same position or area in space(noun.attribute)

  Example:
  He waited for the coincidence of the target and the cross hairs.
  

  source: wordnet30
• the temporal property of two things happening at the same time(noun.attribute)

  Example:
  The interval determining the coincidence gate is adjustable.
  

  Synonym:
  co-occurrence, concurrence, conjunction
  

  source: wordnet30
• The condition of occupying the same place in space; as, the coincidence of circles, surfaces, etc.(noun)

  source: webster1913