Cou"ma*rin (k&oomac;"m&adot;*r&ibreve;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.