'Horseweed' definitions:

Erect perennial strong-scented with serrate pointed leaves and a loose panicle of yellowish flowers; the eastern United States [syn: horse balm, horseweed, stoneroot, stone-root, richweed, stone root, Collinsonia canadensis]

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, Erigeron canadensis]