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.
1650-60;rag1 + weed1, so called from its ragged appearance
For example, melon contains substances similar to ragweed pollen, and apples have allergens similar to tree pollen.
Injections for ragweed and, sometimes, dust mites have higher risks for side effects than other allergy shots.
Thus in a few weeks ragweed plants produce billions of pollen grains, casting them to the winds and to runny noses.
Immunotherapy involves subjecting patients to increasing amounts of ragweed or other compounds to which they are allergic.
British Dictionary definitions for ragweed
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 fever Also called ambrosia