/ Dictionary / Index P phthalic acid: Meaning and Definition of Find definitions for: phthal'ic ac'id Pronunciation: [key] any of three isomeric acids having the formula CHO, esp. the ortho isomera colorless, crystalline, slightly water-soluble solid used chiefly in the manufacture of dyes, medicine, and perfume. See See Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. phthalic phthalic anhydride Related Content Daily Word Quiz: careening Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language