n. any of various small venomous snakes, esp. the common viper, Vipera berus, the only poisonous snake in Great Britain.
Phrases and idioms:
adder's tongue any fern of the genus Ophioglossum.
Etymology: OE n{aelig}dre: n lost in ME by wrong division of a naddre: cf. APRON, AUGER, UMPIRE