/ Dictionary / Index H hydrothermal: Meaning and Definition of Find definitions for: hy•dro•ther•mal Pronunciation: (hī"dru-thûr'mul), [key] — adj. Geol. noting or pertaining to the action of hot, aqueous solutions or gases within or on the surface of the earth. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. hydrotherapy hydrothermal vent Related Content Daily Word Quiz: gregarious Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language