This adjective marks something as deadly or fatal—capable of bringing death. Classical usage applied it to mortal wounds, poisonous snakes, fatal diseases, and capital crimes. It could describe both the inherently lethal (like certain poisons) and the potentially fatal (like serious injuries). Mark uses it in the longer ending to describe deadly poison that won't harm believers who drink it. The term emphasizes not mere danger but actual death-dealing capacity, the power to terminate life.