/ Dictionary / Index R radiothorium: Meaning and Definition of Find definitions for: ra•di•o•tho•ri•um Pronunciation: (rā"dē-ō-thôr'ē-um, -thōr'-), [key] — n. Chem. a disintegration product of thorium. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: radiothorium (Thesaurus) radiothon radiotoxic Related Content Daily Word Quiz: dissonant Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language