The Collaborative International Dictionary of English v.0.48:

Belligerent \Bel*lig"er*ent\, n.
   A nation or state recognized as carrying on war; a person
   engaged in warfare.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Belligerent \Bel*lig"er*ent\, a. [L. bellum war + gerens,
   -entis, waging, p. pr. of gerere to wage: cf. F.
   bellig['e]rant. See Bellicose, Jest.]
   1. Waging war; carrying on war. "Belligerent powers." --E.
      Everett.
      [1913 Webster]

   2. Pertaining, or tending, to war; of or relating to
      belligerents; as, a belligerent tone; belligerent rights.
      [1913 Webster]

WordNet (r) 3.0 (2006):

belligerent
    adj 1: characteristic of an enemy or one eager to fight;
           "aggressive acts against another country"; "a belligerent
           tone" [syn: aggressive, belligerent]
    2: engaged in war; "belligerent (or warring) nations" [syn:
       belligerent, militant, war-ridden, warring]
    n 1: someone who fights (or is fighting) [syn: combatant,
         battler, belligerent, fighter, scrapper]

Moby Thesaurus II by Grady Ward, 1.0:

148 Moby Thesaurus words for "belligerent":
   acrid, aggressive, antagonist, antagonistic, antipathetic, ardent,
   argumental, argumentative, attacking, battler, battling, bellicose,
   belted knight, bickerer, bickering, bitter, blade, bloodthirsty,
   bloody, bloody-minded, bravo, brawler, bully, bullyboy,
   cat-and-dog, cat-and-doggish, caustic, chauvinist, chauvinistic,
   clashing, colliding, combatant, combative, competitor, conflicting,
   contender, contentious, contestant, controversial, despiteful,
   disputant, disputatious, divisive, duelist, enemy, enforcer,
   eristic, factional, factious, fencer, ferocious, feuder, fierce,
   fighter, fighting, fighting cock, foilsman, full of fight,
   full of hate, gamecock, gladiator, goon, gorilla, hatchet man,
   hateful, hawk, hawkish, hood, hoodlum, hooligan, hostile, hot,
   inimical, invading, irascible, irritable, jingo, jingoish,
   jingoist, jingoistic, jouster, knight, litigious, malevolent,
   malicious, malignant, martial, militant, militaristic, military,
   offensive, partisan, plug-ugly, polarizing, polemic, pugnacious,
   quarreler, quarrelsome, rancorous, repugnant, rioter, rival, rough,
   rowdy, ruffian, saber-rattling, sabreur, sanguinary, sanguineous,
   savage, scrapper, scrappy, scuffler, set against, shrewish,
   soldierlike, soldierly, sore, spiteful, squabbler, strong arm,
   strong-arm man, strong-armer, struggler, swashbuckler, sword,
   swordplayer, swordsman, tempered, thug, tilter, tough,
   trigger-happy, truculent, tussler, unfriendly, unpacific,
   unpeaceable, unpeaceful, venomous, virulent, vitriolic, warlike,
   warmonger, warmongering, warring, wrangler, wrangling