Word Study
knapweed
CIDE DICTIONARY
knapweed, n.
The black centaury (Centaurea nigra ); -- so called from the knoblike heads of flowers. Called also bullweed . [1913 Webster]
OXFORD DICTIONARY
knapweed, n. any of various plants of the genus Centaurea, having thistle-like purple flowers.
Etymology
ME, orig. knopweed f. KNOP + WEED
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