/ Dictionary / Index R radioiron: Meaning and Definition of Find definitions for: ra•di•o•i•ron Pronunciation: (rā"dē-ō-ī'urn), [key] — n. Chem. the radioactive isotope of iron, with atomic weight 59 and a half-life of 46 days: used chiefly as a tracer in biochemistry. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. radioiodine radioisotope Related Content Daily Word Quiz: portent Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language