/ Dictionary / Index H hypophosphoric acid: Meaning and Definition of Find definitions for: hy'pophosphor'ic ac'id Pronunciation: [key] a tetrabasic acid, HPO, produced by the slow oxidation of phosphorous in moist air. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. hypophosphoric hypophosphorous Related Content Daily Word Quiz: cygnet Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language