/ Dictionary / Index A adder: Meaning and Definition of Find definitions for: ad•der Pronunciation: (ad'ur), [key] — n. the common European viper, Vipera berus. any of various other venomous or harmless snakes resembling the viper. add•er Pronunciation: (ad'ur), [key] — n. a person or thing that adds. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: adder (Thesaurus) addendum adder's-mouth Related Content Daily Word Quiz: ounterfeit Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language