Either of two plants of the genus Polygonum: (a) knotgrass, P. aviculare (English regional (northern) in later use); (b) US smartweed, P. pennsylvanicum.
Origin
Mid 17th century; earliest use found in William Coles (1626–1662), botanist. From pink + weed.
Definition of pinkweed in US English:
pinkweed
nounˈpɪŋkwiːd
Either of two plants of the genus Polygonum: (a) knotgrass, P. aviculare (English regional (northern) in later use); (b) US smartweed, P. pennsylvanicum.
Origin
Mid 17th century; earliest use found in William Coles (1626–1662), botanist. From pink + weed.