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See more synonyms for radioactive on Thesaurus.com
adjective Physics, Chemistry.
  1. of, pertaining to, exhibiting, or caused by radioactivity.
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Origin of radioactive

First recorded in 1895–1900; radio- + active
Related formsra·di·o·ac·tive·ly, adverbnon·ra·di·o·ac·tive, adjectiveun·ra·di·o·ac·tive, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Related Words for radioactive

dangerous, hot, contaminated, energetic

Examples from the Web for radioactive

Contemporary Examples of radioactive

Historical Examples of radioactive

  • But in order for radioactive breakdown to occur, time must pass.

    Equation of Doom

    Gerald Vance

  • "Eighty-five isn't nearly as radioactive as the elements akin to it," he said.

  • You see, the radioactive planets your men reported, one of them was—home.

    Alien Offer

    Al Sevcik

  • The hull was probably too radioactive to approach from the outside.

    The Lani People

    J. F. Bone

  • They said she was radioactive, but most of 'em wouldn't believe it.

British Dictionary definitions for radioactive


  1. exhibiting, using, or concerned with radioactivity
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Derived Formsradioactively, 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

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).

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Online Etymology Dictionary, © 2010 Douglas Harper

radioactive in Medicine


  1. Of or exhibiting radioactivity.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

radioactive in Culture


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

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