The Collaborative International Dictionary of English v.0.48:

IAA \IAA\ n.
   Indoleacetic acid, a plant hormone promoting elongation of
   stems and roots. [Acronym]

   Syn: indoleacetic acid.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

IAA
    n 1: a plant hormone promoting elongation of stems and roots
         [syn: indoleacetic acid, IAA]
    2: Yemen-based terrorist group that supports al-Qaeda's goals;
       seeks to overthrow the Yemeni government and eliminate United
       States interests; responsible for bombings and kidnappings
       and killing western tourists in Yemen [syn: Islamic Army of
       Aden, IAA, Islamic Army of Aden-Abyan, Aden-Abyan
       Islamic Army]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

IAA
       Intel Application Accelerator


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

IAA
       Initial Address Acknowledgment