/ Dictionary / Index T thallous: Meaning and Definition of Find definitions for: thal•lous Pronunciation: (thal'us), [key] — adj. Chem. containing univalent thallium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. thallophyte thallus Related Content Daily Word Quiz: impetuous Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language