bʰelh₂-
“to strike, fight in battle”rebel, bellicose, belligerent, duel
Root yielding Latin bellum, English rebel, bellicose, belligerent, duel.
Discussion
The PIE root *bʰelh₂- (to strike, to fight, to hit) produced descendants in multiple branches that preserve the original violence of the image — words for beating, fighting, striking, and the noise that accompanies impact.
Latin dēfellāre and the better-attested compound dēbellāre (to fight down, to conquer) continue the root through Latin bellum (war — earlier duellum, from *dwi-bʰelh₂-om, literally a "two-fight," a conflict between two parties). The re-analysis of duellum as bellum (with loss of the initial syllable) is one of the most consequential phonological changes in Latin: it gave the Western world its word for war and generated bellicose (warlike), belligerent (waging war), antebellum (before the war), rebel (re-bellāre, to wage war again), and the personal name Bellatrix (female warrior, also a star in Orion).
The Germanic branch preserves the root in a different semantic register. Old English belt (belt — originally a strap for striking, related to the act of belting/hitting) and the verb beat (OE bēatan, from a related formation) continue the "strike" sense. The word balk (a beam, an obstruction — from the image of a striking/blocking timber) may be connected.
Old Irish at-bailí (he dies) and the related fo-fera (he strikes) provide Celtic attestation. The Irish connection between striking and dying — to die is to be struck — preserves a conceptual link found in multiple IE branches.
Greek phallós (φαλλός, "penis" — etymologically "the swollen/striking thing") is sometimes connected to this root, though the derivation is debated. If correct, the connection would be through the "swelling/protruding" sense of striking — what strikes out, what projects.
The sound-symbolism of the root is worth noting: *bʰelh₂- with its initial labial stop and lateral resonant mimics the sound of a blow — the explosive onset followed by the ringing aftermath. Many IE roots for striking and hitting show similar phonological shapes (*pleh₂g-, *bhew-, *kew-), suggesting that sound-symbolism may have played a role in the original formation of PIE vocabulary for violent impact.