Source : Webster's Revised Unabridged Dictionary (1913)

Coumarin \Cou"ma*rin\ (k[=oo]"m[.a]*r[i^]n), n. [F., fr.
   coumarou, a tree of Guiana.] (Chem.)
   The concrete essence of the tonka bean, the fruit of
   {Dipterix (formerly Coumarouna) odorata} and consisting
   essentially of coumarin proper, which is a white crystalline
   substance, {C9H6O2}, of vanilla-like odor, regarded as an
   anhydride of coumaric acid, and used in flavoring. Coumarin
   in also made artificially.