The Collaborative International Dictionary of English v.0.48:

Gladiator \Glad"i*a`tor\, n. [L., fr. gladius sword. See
   Glaive.]
   1. Originally, a swordplayer; hence, one who fought with
      weapons in public, either on the occasion of a funeral
      ceremony, or in the arena, for public amusement.
      [1913 Webster]

   2. One who engages in any fierce combat or controversy.
      Gladiatorial

WordNet (r) 3.0 (2006):

gladiator
    n 1: (ancient Rome) a professional combatant or a captive who
         entertained the public by engaging in mortal combat
    2: a professional boxer [syn: prizefighter, gladiator]

Moby Thesaurus II by Grady Ward, 1.0:

55 Moby Thesaurus words for "gladiator":
   battler, belligerent, belted knight, bickerer, blade, bravo,
   brawler, bully, bullyboy, combatant, competitor, contender,
   contestant, disputant, duelist, enforcer, fencer, feuder, fighter,
   fighting cock, foilsman, gamecock, 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