Source : Webster's Revised Unabridged Dictionary (1913)

Duel \Du"el\, n. [It. duello, fr. L. duellum, orig., a contest
   between two, which passed into the common form bellum war,
   fr. duo two: cf. F. duel. See {Bellicose}, {Two}, and cf.
   {Duello}.]
   A combat between two persons, fought with deadly weapons, by
   agreement. It usually arises from an injury done or an
   affront given by one to the other.

   {Trial by duel} (Old Law), a combat between two persons for
      proving a cause; trial by battel.