| horseweed | (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. Conyza canadensis, Erigeron canadensis, fleabane, Canadian fleabane |
| Horseweed | n. (Bot.) A composite plant (Erigeron Canadensis), which is a common weed. [ 1913 Webster ] |