/ Dictionary / Index T thermal spring: Meaning and Definition of Find definitions for: ther'mal spring' Pronunciation: [key] a spring whose temperature is higher than the mean temperature of ground water in the area. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. thermal radiation thermal underwear Related Content Daily Word Quiz: wizened Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language