indoleacetic acid \in"dole*a*cet"ic ac"id\ ([i^]n"d[=o]l), n. (Chem., Bot.) A plant hormone ({C10H9NO2}) recognized as the principle growth regulator in higher plants; called also {heteroauxin}. Abbreviated {IAA}. Chemically it is 1H-indole-3-acetic acid. [PJC]