any of several weedy plants (genus Centaurea) of the composite family; esp., a hardy perennial (C. nigra) with heads of rose-purple flowers
Origin of knapweedearlier knopweed: see knop and amp; weed
Any of various weedy thistlelike plants in the composite family having flowers grouped in a head with a spiny involucre, especially several species of the genus Centaurea and the Eurasian species Acroptilon repens.
Origin of knapweedMiddle English knopwed : knop, knob; see knop + wed, weed; see weed1.
Alteration of knopweed.