Definition of adder's grass in English:

adder's grass

noun

obsolete historical
rare
  • Any of several plants thought to resemble a snake in some way, or used to treat snakebites; especially adder's tongue, genus Ophioglossum, and †bistort, Persicaria bistorta (obsolete); compare adderwort. Now historical and rare.

Origin

Late Middle English; earliest use found in Medical Recipes. In some forms from adder + grass. In some forms from the genitive of adder + grass.

Pronunciation:

adder's grass

/ˈadəz ˌɡras//ˈadəz ˌɡrɑːs/