ragweed

noun

1. widespread European weed having yellow daisylike flowers; sometimes an obnoxious weed and toxic to cattle if consumed in quantity

   noun.plant

   Synonyms benweed ragwort senecio jacobaea tansy ragwort

   Source: WordNet 3.0

2. any of numerous chiefly North American weedy plants constituting the genus Ambrosia that produce highly allergenic pollen responsible for much hay fever and asthma

   noun.plant

   Synonyms ambrosia bitterweed

   Source: WordNet 3.0

3. A common American composite weed (<i>Ambrosia artemisi&aelig;folia</i>) with finely divided leaves; hogweed.

   noun

   Source: webster1913