The Collaborative International Dictionary of English v.0.48:

Emodin \Em"o*din\, n. (Chem.)
   An orange-red crystalline substance, C15H10O5, obtained
   from the buckthorn, rhubarb, etc., and regarded as a
   derivative of anthraquinone; -- so called from a species of
   rhubarb (Rheum emodei).
   [1913 Webster]