Source : Webster's Revised Unabridged Dictionary (1913)

Hogweed \Hog"weed`\, n. (Bot.)
   (a) A common weed ({Ambrosia artemisi[ae]ge}). See
       {Ambrosia}, 3.
   (b) In England, the {Heracleum Sphondylium}.

Source : WordNet®

Heracleum sphondylium
     n : tall coarse plant having thick stems and cluster of white to
         purple flowers [syn: {cow parsnip}, {hogweed}]