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):

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