ragweed

noun

1. any of the composite plants of the genus Ambrosia, the airborne pollen of which is the most prevalent cause of autumnal hay fever, as the common North American species, A. trifida (great ragweed or giant ragweed) and A. artemisiifolia.

noun

1. any plant of the chiefly North American genus Ambrosia, such as A. artemisiifolia (common ragweed): family Asteraceae (composites). Their green tassel-like flowers produce large amounts of pollen, which causes hay feverAlso called: ambrosia

n.

1790, from ragged + weed (n.); so called from shape of the leaves. Applied to a different plant (ragwort) from 1650s.

n.

1. Any of various weeds of the genus Ambrosia having small greenish unisexual flower heads and producing abundant pollen that is one of the chief causes of hay fever.