Definition of water horehound in English:

water horehound

noun

  • Any of various plants of the genus Lycopus (family Lamiaceae), which comprises perennial herbaceous plants of wetland habitats, with serrate or deeply cut leaves and whitish, four-lipped flowers borne in whorls in the leaf axils; especially L. europaeus.

Origin

Late 16th century; earliest use found in Henry Lyte (1529–1607), botanist and antiquary.