/ Dictionary / Index H hydronaut: Meaning and Definition of Find definitions for: hy•dro•naut Pronunciation: (hī'dru-nôt", -not"), [key] — n. a person trained to work in deep-sea vessels for research and rescue purposes. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. hydromulch hydronephrosis Related Content Daily Word Quiz: cacophony Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language