phthalic acid

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The colorless crystalline ortho-isomer of benzene dicarboxylic acid, C₈H₆O₂, used in the synthesis of dyes, perfumes, and other organic compounds.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun organic chemistry Any of three isomeric aromatic organic dicarboxylic acids, C6H4(COOH)2; especially the ortho- isomer manufactured from naphthalene, used in the synthesis of dyes, perfumes and other compounds.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a colorless acid used to make dyes and perfumes