1 a any of various plants of the genus Rheum, esp. R. rhaponticum, producing long fleshy dark-red leaf-stalks used cooked as food. b the leaf-stalks of this.
2 a a root of a Chinese and Tibetan plant of the genus Rheum. b a purgative made from this.
3 a colloq. a murmurous conversation or noise, esp. the repetition of the word 'rhubarb' by crowd actors. b sl. nonsense; worthless stuff.
4 US sl. a heated dispute.
Etymology: ME f. OF r(e)ubarbe, shortening of med.L r(h)eubarbarum, alt. (by assoc. with Gk rheon rhubarb) of rhabarbarum foreign 'rha', ult. f. Gk rha + barbaros foreign
Useful english dictionary. 2012.