The Collaborative International Dictionary of English v.0.48:

Duelist \Du"el*ist\, n. [F. duelliste.]
   One who fights in single combat. [Written also duellist.]
   [1913 Webster]

         A duelist . . . always values himself upon his courage,
         his sense of honor, his fidelity and friendship.
                                                  --Hume.
   [1913 Webster]

WordNet (r) 3.0 (2006):

duelist
    n 1: a person who fights duels [syn: dueler, dueller,
         duelist, duellist]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "duelist":
   battler, belligerent, belted knight, bickerer, blade, bravo,
   brawler, bully, bullyboy, combatant, competitor, contender,
   contestant, disputant, enforcer, fencer, feuder, fighter,
   fighting cock, foilsman, gamecock, gladiator, goon, gorilla,
   hatchet man, hood, hoodlum, hooligan, jouster, knight, militant,
   plug-ugly, quarreler, rioter, rival, rough, rowdy, ruffian,
   sabreur, scrapper, scuffler, squabbler, strong arm, strong-arm man,
   strong-armer, struggler, swashbuckler, sword, swordplayer,
   swordsman, thug, tilter, tough, tussler, wrangler