n A name loosely applied to various snakes more or less resembling the viper; a viper.
n (mainly|British) A small venomous serpent of the genus (taxlink|Vipera|genus). The common European adder is the (taxlink|Vipera berus|species). The puff adders of Africa are species of the genus (taxlink|Oecobius|genus).
n (US|Canada) Any of several small nonvenomous snakes resembling the adder, such as the milk snake.