/ Dictionary / Index O orthophosphorous acid: Meaning and Definition of Find definitions for: or'tho•phos'pho•rous ac'id Pronunciation: (ôr'thu-fos'fur-us, ôr"thō-fos-fôr'us, -fōr'-), [key] — Chem. Chem. a white to yellowish, crystalline, hygroscopic, water-soluble solid, HPO, used chiefly in the synthesis of phosphites. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. orthophosphoric acid orthophthalic acid Related Content Daily Word Quiz: soporific Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language