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[rey-dee-oh-ak-tiv] /ˌreɪ di oʊˈæk tɪv/
adjective, Physics, Chemistry
of, pertaining to, exhibiting, or caused by radioactivity.
Origin of radioactive
1895-1900; radio- + active
Related forms
radioactively, adverb
nonradioactive, adjective
unradioactive, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for radioactive
  • The raindrops that keep falling on our heads may not cause our hair to fall out but they are, nevertheless, radioactive.
  • It would also not itself become radioactive by absorbing neutrons.
  • Around the world radioactive nuclear reactors in derelict submarines dot the seafloor.
  • radioactive sulphur signal adds to evidence of catastrophe.
  • Years later, they discovered two radioactive elements.
  • radioactive abscess scan uses a radioactive substance to look for abscesses in the body.
  • But the world has a short attention span, whereas the half-lives of many radioactive isotopes are long indeed.
  • Painting yourself with iodine is an imprecise way to protect yourself if you are exposed to radioactive iodine, but it can work.
  • Few knew the danger of radioactive materials at the time.
  • Mechanism by which microbes scrub radioactive contamination revealed.
British Dictionary definitions for radioactive


exhibiting, using, or concerned with radioactivity
Derived Forms
radioactively, adverb
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
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Word Origin and History for radioactive

1898, from French radio-actif, coined by Pierre and Marie Curie from radio-, comb. form of Latin radius (see radiation) + actif "active" (see active).

Online Etymology Dictionary, © 2010 Douglas Harper
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radioactive in Medicine

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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radioactive in Culture

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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