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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
First recorded in 1895-1900; radio- + active
Related forms
radioactively, adverb
nonradioactive, adjective
unradioactive, adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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Examples from the Web for radioactive
Contemporary Examples
Historical Examples
  • 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.

    The Onslaught from Rigel Fletcher Pratt
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 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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