The Collaborative International Dictionary of English v.0.48:

Plumbagin \Plum*ba"gin\ (pl[u^]m*b[=a]"j[i^]n), n. [L. plumbago
   leadwort, fr. plumbum lead; cf. F. plombagin.] (Chem.)
   A crystalline substance said to be found in the root of a
   certain plant of the Leadwort (Plumbago) family.
   [1913 Webster]