adjective Physics, Chemistry.
of, pertaining to, exhibiting, or caused by radioactivity.

1895–1900; radio- + active

radioactively, adverb
nonradioactive, adjective
unradioactive, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
radioactive (ˌreɪdɪəʊˈæktɪv)
exhibiting, using, or concerned with radioactivity

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1898, from Fr. radio-actif, coined by Pierre and Marie Curie from radio-, comb. form of L. radius (see radiation) + actif (fem. active) "active."
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

radioactive ra·di·o·ac·tive (rā'dē-ō-āk'tĭv)
Of or exhibiting radioactivity.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Cultural Dictionary

radioactive definition

A descriptive term for a material made up of atoms in which radioactivity occurs.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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