/ Dictionary / Index R radioiodine: Meaning and Definition of Find definitions for: ra•di•o•i•o•dine Pronunciation: (r?"d?-?-?'u-d?n", -din, -d?n"), [key] ? n. Chem. any of nine radioisotopes of iodine, esp. iodine 131 and iodine 125, used as radioactive tracers in research and clinical diagnosis and treatment. Random House Unabridged Dictionary, Copyright 1997, by Random House, Inc., on Infoplease. radio interferometer radioiron Related Content Daily Word Quiz: abdicate Analogy of the Day: Today?s Analogy Spelling Bee: Today?s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language