The Collaborative International Dictionary of English v.0.48:

Hogweed \Hog"weed`\, n. (Bot.)
      (a) A common weed (Ambrosia artemisi[ae]ge). See
          Ambrosia, 3.
      (b) In England, the Heracleum Sphondylium.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cow parsnip \Cow" pars`nip\ (-n?p). (Bot.)
   A coarse umbelliferous weed of the genus Heracleum
   (Heracleum sphondylium in England, and Heracleum lanatum
   in America).
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Bear's-breech \Bear's"-breech`\, bear's-breeches
\bear's"-breech`es\, n.
   1. (Bot.) The English cow parsnip (Heracleum sphondylium)
      --Dr. Prior.
      [1913 Webster]

   2. a widely cultivated southern European acanthus (Acanthus
      mollis) with whitish purple-veined flowers. See
      Acanthus, n., 1.

   Syn: bear's breech, bear's-breech, bear's breeches, sea
        holly.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Heracleum sphondylium
    n 1: tall coarse plant having thick stems and cluster of white
         to purple flowers [syn: cow parsnip, hogweed,
         Heracleum sphondylium]