ad·der noun \ˈad-ər\
: the common venomous European viper of the genus Vipera (V. berus); broadly : a terrestrial viper of the family Viperidae
: any of several North American snakes (as the hognose snakes) that are harmless but are popularly believed to be venomous
Seen & Heard
What made you want to look up adder? Please tell us where you read or heard it (including the quote, if possible).