The Collaborative International Dictionary of English v.0.48:

Duel \Du"el\, v. i. & t.
   To fight in single combat. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

   Trial by duel (Old Law), a combat between two persons for
      proving a cause; trial by battel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

duel
    n 1: a prearranged fight with deadly weapons by two people
         (accompanied by seconds) in order to settle a quarrel over
         a point of honor [syn: duel, affaire d'honneur]
    2: any struggle between two skillful opponents (individuals or
       groups)
    v 1: fight a duel, as over one's honor or a woman; "In the 19th
         century, men often dueled over small matters"

Moby Thesaurus II by Grady Ward, 1.0:

51 Moby Thesaurus words for "duel":
   affair of honor, battle, box, brawl, broil, buck, clash, close,
   collide, combat, come to blows, contend, contest, cut and thrust,
   dispute, exchange blows, fence, feud, fight, fight a duel,
   give and take, give satisfaction, grapple, grapple with, jostle,
   joust, mix it up, monomachy, oppose, quarrel, rassle, repel, riot,
   run a tilt, satisfaction, scramble, scuffle, single combat,
   skirmish, spar, strive, struggle, thrust and parry, tilt, tourney,
   traverse, tussle, wage war, war, withstand, wrestle



The Free On-line Dictionary of Computing (30 December 2018):

DUEL

    A front end to gdb by Michael Golan
   .  DUEL implements a language designed
   for debugging C programs.  It features efficient ways to
   select and display data items.  It is normally linked into the
   gdb executable, but could stand alone.  It interprets a subset
   of C in addition to its own language.

   Version 1.10.

   (ftp://ftp.cs.princeton.edu/duel/).

   (1993-03-20)


The Devil's Dictionary (1881-1906):

DUEL, n.  A formal ceremony preliminary to the reconciliation of two
enemies.  Great skill is necessary to its satisfactory observance; if
awkwardly performed the most unexpected and deplorable consequences
sometimes ensue.  A long time ago a man lost his life in a duel.

    That dueling's a gentlemanly vice
        I hold; and wish that it had been my lot
        To live my life out in some favored spot --
    Some country where it is considered nice
    To split a rival like a fish, or slice
        A husband like a spud, or with a shot
        Bring down a debtor doubled in a knot
    And ready to be put upon the ice.
    Some miscreants there are, whom I do long
        To shoot, to stab, or some such way reclaim
    The scurvy rogues to better lives and manners,
    I seem to see them now -- a mighty throng.
        It looks as if to challenge _me_ they came,
    Jauntily marching with brass bands and banners!
                                                          Xamba Q. Dar