(1):

(n.) One who, or that which, adds; esp., a machine for adding numbers.

(2):

(n.) A serpent.

(3):

(n.) A small venomous serpent of the genus Vipera. The common European adder is the Vipera (/ Pelias) berus. The puff adders of Africa are species of Clotho.

(4):

(n.) In America, the term is commonly applied to several harmless snakes, as the milk adder, puffing adder, etc.

(5):

(n.) Same as Sea Adder.