/ Dictionary / Index T thallium sulfate: Meaning and Definition of Find definitions for: thal'lium sul'fate Pronunciation: [key] — Chem. Chem. a colorless, crystalline, water-soluble, poisonous solid, TlSO, used chiefly as an insecticide and rodenticide. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. thallium thalloid 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