any of several plants belonging to the genus Rheum, of the buckwheat family, as R. officinale, having a medicinal rhizome, and R. rhabarbarum, having edible leafstalks.
the rhizome of any medicinal species of this plant, forming a combined cathartic and astringent.
the edible, fleshy leafstalks of R. rhabarbarum, used in making pies, preserves, etc.