The Collaborative International Dictionary of English v.0.48:

disputant \dis"pu*tant\, a. [L. disputants, p. pr. of disputare:
   cf. F. disputant. See Dispute, v. i.]
   Disputing; engaged in controversy. --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

disputant \dis"pu*tant\, n.
   One who disputes; one who argues in opposition to another;
   one appointed to dispute; a controvertist; a reasoner in
   opposition.
   [1913 Webster]

         A singularly eager, acute, and pertinacious disputant.
                                                  --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

disputant
    n 1: a person who disputes; who is good at or enjoys controversy
         [syn: disputant, controversialist, eristic]

Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "disputant":
   Philadelphia lawyer, apologist, arguer, argufier, battler,
   belligerent, belted knight, bickerer, bitter-ender, blade, bravo,
   brawler, bully, bullyboy, casuist, combatant, competitor,
   contender, contestant, controversialist, debater, defendant,
   diehard, disceptator, dissentient, dissident, duelist, enforcer,
   fencer, feuder, fighter, fighting cock, foilsman, gamecock,
   gladiator, goon, gorilla, guardhouse lawyer, hatchet man, hood,
   hoodlum, hooligan, intransigent, irreconcilable, jouster, knight,
   last-ditcher, litigant, logomacher, logomachist, militant, mooter,
   naysayer, negativist, noncooperator, objector, obstructionist,
   obstructive, opposer, oppositionist, pilpulist, plaintiff,
   plug-ugly, polemic, polemicist, polemist, protester, quarreler,
   resister, 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