Webster's Revised Unabridged Dictionary · 1913

Phthalic

Phthalic , adjective

[Naphthalene + -ic.]

(Chemistry) Pertaining to, or designating, a dibasic acid obtained by the oxidation of naphthalene and allied substances.
Collocations (1)
Phthalic acid (Chemistry) , a white crystalline substance, C6H4.(CO2H)2, analogous to benzoic acid, and employed in the brilliant dyestuffs called the phthaleins.