Source : Webster's Revised Unabridged Dictionary (1913)

Rhubarb \Rhu"barb\, n. [F. rhubarbe, OF. rubarbe, rheubarbe,
   reubarbare, reobarbe, LL. rheubarbarum for rheum barbarum,
   Gr. ??? (and ??) rhubarb, from the river Rha (the Volga) on
   whose banks it grew. Originally, therefore, it was the
   barbarian plant from the Rha. Cf. {Barbarous},
   {Rhaponticine}.]
   1. (Bot.) The name of several large perennial herbs of the
      genus {Rheum} and order {Polygonace[ae]}.

   2. The large and fleshy leafstalks of {Rheum Rhaponticum} and
      other species of the same genus. They are pleasantly acid,
      and are used in cookery. Called also {pieplant}.

   3. (Med.) The root of several species of {Rheum}, used much
      as a cathartic medicine.

   {Monk's rhubarb}. (Bot.) See under {Monk}.

   {Turkey rhubarb} (Med.), the roots of {Rheum Emodi}.

Source : WordNet®

rhubarb
     n 1: long pinkish sour leafstalks usually eaten cooked and
          sweetened [syn: {pieplant}]
     2: plants having long green or reddish acidic leafstalks
        growing in basal clumps; stems (and only the stems) are
        edible when cooked; leaves are poisonous [syn: {rhubarb
        plant}]