The Collaborative International Dictionary of English v.0.48:

Parsnip \Pars"nip\ (p[aum]rs"n[i^]p), n. [OE. parsnepe, from a
   French form, fr. L. pastinaca; cf. pastinare to dig up,
   pastinum a kind of dibble; cf. OF. pastenade, pastenaque.]
   (Bot.)
   The aromatic and edible spindle-shaped root of the cultivated
   form of the Pastinaca sativa, a biennial umbelliferous
   plant which is very poisonous in its wild state; also, the
   plant itself.
   [1913 Webster]

   Cow parsnip. See Cow parsnip.

   Meadow parsnip, the European cow parsnip.

   Poison parsnip, the wild stock of the parsnip.

   Water parsnip, any plant of the umbelliferous genus Sium,
      the species of which are poisonous.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Masterwort \Mas"ter*wort`\, n. (Bot.)
   (a) A tall and coarse European umbelliferous plant
       (Peucedanum Ostruthium, formerly Imperatoria).
   (b) The Astrantia major, a European umbelliferous plant
       with a showy colored involucre.
   (c) Improperly, the cow parsnip (Heracleum lanatum).
       [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]

WordNet (r) 3.0 (2006):

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