from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A radioactive isotope of iodine widely used as a tracer in medical diagnosis.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. (medicine) The radioactive isotope of iodine, 13153I, having a half-life of 8 days; used as a medical tracer
radio- + iodine (Wiktionary)