The Collaborative International Dictionary of English v.0.48:

Accident \Ac"ci*dent\, n. [F. accident, fr. L. accidens,
   -dentis, p. pr. of accidere to happen; ad + cadere to fall.
   See Cadence, Case.]
   1. Literally, a befalling; an event that takes place without
      one's foresight or expectation; an undesigned, sudden, and
      unexpected event; chance; contingency; often, an
      undesigned and unforeseen occurrence of an afflictive or
      unfortunate character; a casualty; a mishap; as, to die by
      an accident.
      [1913 Webster]

            Of moving accidents by flood and field. --Shak.
      [1913 Webster]

            Thou cam'st not to thy place by accident:
            It is the very place God meant for thee. --Trench.
      [1913 Webster]

   2. (Gram.) A property attached to a word, but not essential
      to it, as gender, number, case.
      [1913 Webster]

   3. (Her.) A point or mark which may be retained or omitted in
      a coat of arms.
      [1913 Webster]

   4. (Log.)
      (a) A property or quality of a thing which is not
          essential to it, as whiteness in paper; an attribute.
      (b) A quality or attribute in distinction from the
          substance, as sweetness, softness.
          [1913 Webster]

   5. Any accidental property, fact, or relation; an accidental
      or nonessential; as, beauty is an accident.
      [1913 Webster]

            This accident, as I call it, of Athens being
            situated some miles from the sea.     --J. P.
                                                  Mahaffy.
      [1913 Webster]

   6. Unusual appearance or effect. [Obs.] --Chaucer.
      [1913 Webster]

   Note: Accident, in Law, is equivalent to casus, or such
         unforeseen, extraordinary, extraneous interference as
         is out of the range of ordinary calculation.
         [1913 Webster]

WordNet (r) 3.0 (2006):

accident
    n 1: an unfortunate mishap; especially one causing damage or
         injury
    2: anything that happens suddenly or by chance without an
       apparent cause; "winning the lottery was a happy accident";
       "the pregnancy was a stroke of bad luck"; "it was due to an
       accident or fortuity" [syn: accident, stroke, fortuity,
       chance event]

The Devil's Dictionary (1881-1906):

ACCIDENT, n.  An inevitable occurrence due to the action of immutable
natural laws.