- a common weed (Conyza canadensis) of the composite family, with a wandlike stem and a panicle of many small, greenish-white flower heads
- any of various other weeds
A weedy North American annual plant (Conyza canadensis) in the composite family, having a tall erect stem, narrow leaves, and numerous small whitish flower heads grouped in panicles. Also called mare's tail.
(countable and uncountable, plural horseweeds)