What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
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.
Late 16th century; earliest use found in Henry Lyte (1529–1607), botanist and antiquary.