Webster's Revised Unabridged Dictionary · 1913

Duel

Duel , noun

[Italian duello, from Latin duellum, orig., a contest between two, which passed into the common form bellum war, from duo two: compare French duel. See Bellicose, Two, and compare 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.
Collocations (1)
Trial by duel (Old Law) , a combat between two persons for proving a cause; trial by battel.

Duel , verb, intransitive and transitive

To fight in single combat. [Obsolete]