noun /ˈæd.ɚ/
a) A small venomous serpent of the genus Vipera. The common European adder is the Vipera (or Pelias) berus. The puff adders of Africa are species of the genus Clotho.
They sought out cost adders with an eye toward eliminating them.
b) Any of several small nonvenomous snakes resembling the adder, such as the milk snake.
Wikipedia foundation.