poisonous, venomous, vicious
Meaning: marked by deep ill will; deliberately harmful; "poisonous hate"; "venomous criticism"; "vicious gossip"
deadly, venomous, virulent
Meaning: extremely poisonous or injurious; producing venom; "venomous snakes"; "a virulent insect bite"
The most ferocious carnivores are found in the mountains, and the most venomous serpents haunt the lowlands.
"And we have also learnt that the poison of the Pelagian heresy again springs up among you; we, therefore, exhort you, that you put away from your thoughts all such venomous and superstitious wickedness.