Source : Webster's Revised Unabridged Dictionary (1913)

Chance-medley \Chance"-med`ley\, n. [Chance + medley.]
   1. (Law) The killing of another in self-defense upon a sudden
      and unpremeditated encounter. See {Chaud-Medley}.

   Note: The term has been sometimes applied to any kind of
         homicide by misadventure, or to any accidental killing
         of a person without premeditation or evil intent, but,
         in strictness, is applicable to such killing as happens
         in defending one's self against assault. --Bouvier.

   2. Luck; chance; accident. --Milton. --Cowper.

Source : WordNet®

chance-medley
     n : unpremeditated killing of a human being in self defense