Source : Webster's Revised Unabridged Dictionary (1913)

Casualty \Cas"u*al*ty\, n.; pl. {Casualties}. [F. casualit['e],
   LL. casualitas.]
   1. That which comes without design or without being foreseen;
      contingency.

            Losses that befall them by mere casualty. --Sir W.
                                                  Raleigh.

   2. Any injury of the body from accident; hence, death, or
      other misfortune, occasioned by an accident; as, an
      unhappy casualty.

   3. pl. (Mil. & Naval) Numerical loss caused by death, wounds,
      discharge, or desertion.

   {Casualty ward}, A ward in a hospital devoted to the
      treatment of injuries received by accident.

   Syn: Accident; contingency; fortuity; misfortune.

Source : WordNet®

casualty
     n 1: someone injured or killed or captured or missing in a
          military engagement
     2: someone injured or killed in an accident [syn: {injured
        party}]
     3: an accident that causes someone to die [syn: {fatal accident}]
     4: a decrease of military personnel or equipment