indole UK /ˈɪndəʊl/US /ˈɪndoʊl/noun 2adjective 1forms 3 noun2 •An organic compound, C₈H₇N, found in coal tar, and produced in the gut by the bacterial decomposition of tryptophan; it is an aromatic bicyclic heterocycle having a benzene ring fused with a pyrrole ring; indole and its derivatives occur widely in nature and have many industrial applications.The Aspidosperma alkaloids are the largest group of indole alkaloids. — 1990 •Any of the derivatives of indole. adjective1 •(no longer used) guileless formsindoles · more indole · most indole