Synonyms for Belligerent (same or very similar meaning)
WordNet sense 1 (someone who fights (or is fighting)):
battler, combatant, fighter, scrapper
WordNet sense 2 (engaged in war):
fighting, militant, warring, war-ridden
WordNet sense 3 (not peaceful):
unpeaceful
WordNet sense 4 (characteristic of an enemy or one eager to fight):
aggressive
WordNet sense 5 (characterized by enmity or ill will):
hostile
From the ODE community, based on WordNet
add/edit