Wiktionary(0.00 / 0 votes)Rate this definition: 1  belligerent(Noun) A state or other armed participant in warfare. The U.N. sent a treaty proposal to the belligerents. 2  belligerent(Adjective) Engaged in warfare, warring. 3  belligerent(Adjective) Eager to go to war, warlike.  belligerent(Adjective) Of or pertaining to war.