massacre, annihilation
鏖 centers on total destruction of life: a massacre or complete annihilation, leaving nothing behind.
鏖 combines 鹿 (deer) and 金 (metal). The exact historical development is uncertain, but it likely originally depicted the slaughter of deer with metal weapons, extending to massacre in general.
Picture a deer (鹿) being surrounded and cut down by metal (金) blades, leaving nothing alive. This is total annihilation.
For オウ, imagine the sound of a heavy metal blade swinging through the air: 'ow!' as it strikes, echoing the massacre. 'Ow' -> オウ.