/ Dictionary / Index G geothermal: Meaning and Definition of Find definitions for: ge•o•ther•mal Pronunciation: ( jē"ō-thûr'mul), [key] — adj. of or pertaining to the internal heat of the earth. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: geothermal (Thesaurus) geotectonic geothermal gradient Related Content Daily Word Quiz: pundit Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language