ADDER'S TONGUE Meaning of ADDER'S TONGUE in English ■ noun1》 a fern with a single pointed oval frond and an unbranched spore-bearing stem. [Genus Ophioglossum .] 2》 North American term for dog's-tooth violet . Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004