Phthal″ic (?), a. [Naphthalene + -ic.] (Chem.) Pertaining to, or designating, a dibasic acid obtained by the oxidation of naphthalene and allied substances.
Phthalic acid(Chem.), a white crystalline substance, C6H4.(CO2H)2, analogous to benzoic acid, and employed in the brilliant dyestuffs called the phthaleins.