to destroy, to exterminate, to extinguish
烕 centers on complete destruction: wiping something out, exterminating it, or extinguishing it entirely. The idea is forceful removal or annihilation.
烕 combines 戌 (a weapon or halberd) with 火 (fire), suggesting destruction by weapon and fire. The exact historical development is uncertain, but the component combination clearly conveys extinguishing or destroying.
Outside, a weapon 戌 surrounds a fire 火 inside. Imagine using a blade to snuff out a flame, completely destroying it.
For ケツ, picture a kettle (ケツ) of water being poured over a fire to extinguish it: the kettle's sound cues ケツ, and the fire is destroyed.