The Collaborative International Dictionary of English v.0.48:

Indole \In"dole\, Indol \In"dol\([i^]n"d[=o]l), n. [Indigo + -ol
   of phenol.] (Chem., Physiol. Chem.)
   A white, crystalline substance, C8H7N, obtained from blue
   indigo, and almost all indigo derivatives, by a process of
   reduction; chemically, it is 2,3-benzopyrrole, a bicyclic
   heterocyclic compound, having a benzene ring fused to a
   pyrrole ring. It is also formed from proteinaceous matter,
   together with skatol, by putrefaction, and by fusion with
   caustic potash, and is present in human excrement, as well as
   in the intestinal canal of some herbivora. It is produced in
   rich growth media by the intestinal bacterium Escherichia
   coli.
   [1913 Webster +PJC]