/ Dictionary / Index O orthophthalic acid: Meaning and Definition of Find definitions for: or•tho•phthal'ic ac'id Pronunciation: (ôr"thu-thal'ik, -thuf-thal'-). [key] — Chem. Chem. See under(def. 1). Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. orthophosphorous acid orthophyric Related Content Daily Word Quiz: arid Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language