any of three isomeric acids, CH(COOH), esp. one (ortho-phthalic acid) obtained by oxidation of naphthalene or xylene and used in the manufacture of dyes, medicines, etc.
Origin:
(na)phthal(ene) + -ic
See phthalic acid in American Heritage Dictionary 4
noun
A colorless crystalline organic acid, C6H4(COOH)2, prepared from naphthalene and used in the synthesis of dyes, perfumes, and other organic compounds.