The Collaborative International Dictionary of English v.0.48:

Occurrence \Oc*cur"rence\, n. [Cf. F. occurrence. See Occur.]
   1. A coming or happening; as, the occurrence of a railway
      collision.
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            Voyages detain the mind by the perpetual occurrence
            and expectation of something new.     --I. Watts.
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   2. Any event or incident; esp., one which happens without
      being designed or expected; as, an unusual occurrence, or
      the ordinary occurrences of life.
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            All the occurrence of my fortune.     --Shak.
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   Syn: See Event.
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WordNet (r) 3.0 (2006):

occurrence
    n 1: an event that happens [syn: happening, occurrence,
         occurrent, natural event]
    2: an instance of something occurring; "a disease of frequent
       occurrence"; "the occurrence (or presence) of life on other
       planets"