Any one of numerous species of Old World venomous makes belonging to Vipera, Clotho, Daboia, and other genera of the family Viperidæ.
- Any of several venomous Old World snakes of the family Viperidae, having a single pair of long, hollow fangs and a thick, heavy body. Also called adder2.
- A pit viper.
- A venomous or supposedly venomous snake.
- A person regarded as malicious or treacherous.