chance-med·ley /ˈʧæn(t)sˈmɛdli/
  過失殺傷
  Chance-med·ley n.
  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.
  2. Luck; chance; accident.
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  chance-medley
       n : unpremeditated killing of a human being in self defense