/ Dictionary / Index H hyponitrous acid: Meaning and Definition of Find definitions for: hy'poni'trous ac'id Pronunciation: [key] an unstable, crystalline acid, HNO. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. hyponitrous hyponym 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