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.