Horseweed \Horse"weed`\, n. (Bot.) A composite plant ({Erigeron Canadensis}), which is a common weed.
Erigeron canadensis n : common North American weed with linear leaves and small discoid heads of yellowish flowers; widely naturalized throughout temperate regions; sometimes placed in genus Erigeron [syn: {horseweed}, {Canadian fleabane}, {fleabane}, {Conyza canadensis}]