belligerent (adj.)

early 15c., "inclined to fighting," from Latin bellicosus "warlike, valorous, given to fighting," from bellicus "of war," from bellum "war" (Old Latin duellum, dvellum), which is of uncertain origin.

The best etymology for duellum so far has been proposed by Pinault 1987, who posits a dim. *duelno- to bonus. If *duelno- meant 'quite good, quite brave', its use in the context of war (bella acta, bella gesta) could be understood as a euphemism, ultimately yielding a meaning 'action of valour, war' for the noun bellum. [de Vaan]

"famous deed, exploit," more commonly "story of great deeds, tale of adventure," c. 1300, from Old French geste, jeste "action, exploit, romance, history" (of celebrated people or actions), from Medieval Latin gesta "actions, exploits, deeds, achievements," noun use of neuter plural of Latin gestus, past participle of gerere "to carry on, wage, perform," which de Vaan says is considered to be from the same root as agere "to set in motion, drive forward, do, perform" (from PIE root *ag- "to drive, draw out or forth, move"). Now only as a deliberate archaism. Jest (n.) is the same word, with a decayed sense.