/ Dictionary / Index H hypersonic: Meaning and Definition of Find definitions for: hy•per•son•ic Pronunciation: (hī"pur-son'ik), [key] — adj. noting or pertaining to speed that is at least five times that of sound in the same medium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. hypersomnia hyperspace Related Content Daily Word Quiz: simian Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language