Bellicose and "duel" are secret siblings — Latin bellum (war) evolved from Old Latin duellum (combat between two), losing its 'd' along the way.
Demonstrating aggression and willingness to fight. Inclined toward or favoring war and conflict.
From Latin bellicōsus (warlike), from bellicus (of war), from bellum (war), possibly from an older form duellum (combat between two), from duo (two) Key roots: bellum (Latin: "war"), duellum (Old Latin: "combat, war (originally between two)"), *dwo- (Proto-Indo-European: "two").
Latin bellum (war) is thought to derive from Old Latin duellum (combat between two), which lost its initial 'd' over time. This means "bellicose" and "duel" are etymological cousins — one kept the 'd', the other dropped it. The musical term "bellicoso" is a performance direction meaning "in a warlike manner