Source : Webster's Revised Unabridged Dictionary (1913)

Ragweed \Rag"weed\, n. (Bot.)
   A common American composite weed ({Ambrosia
   artemisi[ae]folia}) with finely divided leaves; hogweed.

   {Great ragweed}, a coarse American herb ({Ambrosia trifida}),
      with rough three-lobed opposite leaves.

Source : WordNet®

great ragweed
     n : a coarse annual with some leaves deeply and palmately
         3-cleft or 5-cleft [syn: {Ambrosia trifida}]