Dictionary.com
definitions

radionuclide

[rey-dee-oh-noo-klahyd, -nyoo-]
noun Physics.
  1. a radioactive nuclide.

Origin of radionuclide

First recorded in 1945–50; radio- + nuclide
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for radionuclide

radionuclide

noun
  1. a nuclide that is radioactive
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
radionuclide in Medicine

radionuclide

[rā′dē-ō-nōō′klīd′]
n.
  1. A nuclide that has artificial or natural origin and that exhibits radioactivity.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
radionuclide in Science

radionuclide

[rā′dē-ō-nōō′klīd′]
  1. A nuclide that exhibits radioactivity.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.