/ Dictionary / Index T thionic: Meaning and Definition of Find definitions for: thi•on•ic Pronunciation: (thī-on'ik), [key] — adj. Chem. of or pertaining to sulfur. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. thiol thionic acid Related Content Daily Word Quiz: resilient Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language