Any of several venomous snakes of the viper family (Viperidae) and the death adder, a viperlike elapid. Vipers include the common adder, puff adders, and night adders. Adders occur in Europe, Asia, Africa, and Australia. They range in length from 18 in. to 5 ft (45 cm to 1.5 m). The puff adder of Africa and the death adder of Australia and the nearby islands are particularly venomous, with a bite potentially lethal to humans. The name is also used for other snakes (e.g., the hognose snake).