Source : Webster's Revised Unabridged Dictionary (1913)

Water parsnip \Wa"ter pars"nip\ (Bot.)
   Any plant of the aquatic umbelliferous genus {Sium},
   poisonous herbs with pinnate or dissected leaves and small
   white flowers.

Parsnip \Pars"nip\, 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.

   {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.

Source : WordNet®

water parsnip
     n : stout white-flowered perennial found wild in shallow fresh
         water; northern United States and Asia [syn: {Sium suave}]