1. (noun)horse balm, horseweed, stoneroot, stone-root, richweed, stone root, Collinsonia canadensis erect perennial strong-scented with serrate pointed leaves and a loose panicle of yellowish flowers; the eastern United States Synonyms: stoneroot, richweed, fleabane, horsebalm, deadnettle, clearweed, stoneroot, horseweed, stone-root