Knap·weed n. Bot. The black centaury (Centaurea nigra); -- so called from the knoblike heads of flowers. Called also bullweed.
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Mat·fel·on n. Bot. The knapweed (Centaurea nigra).
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I·ron·heads n. Bot. A European composite herb (Centaurea nigra); -- so called from the resemblance of its knobbed head to an iron ball fixed on a long handle.
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Centaurea nigra
n : a weedy perennial with tough wiry stems and purple flowers;
native to Europe but widely naturalized [syn: lesser
knapweed, black knapweed, hardheads]