WordNet sense 1 (extremely poisonous or injurious; producing venom):

venomous

WordNet sense 2 (of or relating to or caused by a toxin or poison):

toxic

WordNet sense 3 (involving loss of divine grace or spiritual death):

mortal

WordNet sense 4 (not admitting of pardon):

unpardonable

WordNet sense 5 (exceedingly harmful):

baneful, pernicious, pestilent

WordNet sense 6 (injurious to physical or mental health):

harmful, noxious

WordNet sense 7 (of an instrument of certain death):

lethal

WordNet sense 8 (causing or capable of causing death):

deathly

WordNet sense 9 (bringing death):

fatal

WordNet sense 10 (as if dead):

lifelessly

WordNet sense 11 (infectious; having the ability to cause disease):

virulent

WordNet sense 12 ((used as intensives) extremely):

devilishly, insanely, madly, deucedly