The Collaborative International Dictionary of English v.0.48:

Assailant \As*sail"ant\, a. [F. assaillant, p. pr. of
   assaillir.]
   Assailing; attacking. --Milton.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Assailant \As*sail"ant\, n. [F. assaillant.]
   One who, or that which, assails, attacks, or assaults; an
   assailer.
   [1913 Webster]

         An assailant of the church.              --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

assailant
    n 1: someone who attacks [syn: attacker, aggressor,
         assailant, assaulter]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "assailant":
   adversary, aggressor, antagonist, assailer, assaulter, attacker,
   combatant, enemy, foe, foeman, invader, mugger, opponent,
   opposing party, opposite camp, raider, the loyal opposition,
   the opposition