Any of several aquatic plants with whorls of small leaves around the stem and inconspicuous flowers; especially. Canadian pondweed, Elodea canadensis, and the related waterweed Hydrilla verticillata.
Origin
Mid 17th century (in an earlier sense). From water + thyme.
Definition of water thyme in US English:
water thyme
nounˈwɔːtə ˌtʌɪm
Any of several aquatic plants with whorls of small leaves around the stem and inconspicuous flowers; especially. Canadian pondweed, Elodea canadensis, and the related waterweed Hydrilla verticillata.
Origin
Mid 17th century (in an earlier sense). From water + thyme.