1Any of several rhubarbs (genus Rheum) originating in or obtained from East Asia, especially R. palmatum (also called Chinese rhubarb), often used medicinally for its laxative and astringent properties; an extract or preparation of this. Now chiefly historical.
2North American The umbrella plant, Darmera peltata (family Saxifragaceae).
Mid 17th century; earliest use found in Nicholas Culpeper (1616–1654), physician and astrologer. From Indian + rhubarb.