ra·​dio·​ac·​tive | \ ˌrā-dē-ō-ˈak-tiv How to pronounce radioactive (audio) \

Definition of radioactive

1 : of, caused by, or exhibiting radioactivity radioactive isotopes Radon is an odorless, colorless gas that arises naturally from the ground because of the decay of radioactive elements commonly found in rocks and many types of soil. In a chain of radioactive decay, uranium produces radium, which gives off radon, which in turn produces radioactive breakdown products that are harmful if inhaled.— Warren E. Leary
2 : so divisive or controversial as to require avoidance He has been deemed radioactive by most charitable organizations … and organized competition, even local stuff, is largely closed off to him.— Asher Price Almost all women—and therefore men—use a form of birth control at some point in their lives, yet contraception is so politically and legally radioactive that legislators and pharmaceutical companies avoid funding it.— Karen Weise Subsequent polling data show that the quota issue is perhaps the most powerful one in our politics … A House Democratic aide says, "The quota issue is radioactive." The result has been nothing less than panic in the Democratic ranks.— Elizabeth Drew

Other Words from radioactive

radioactively adverb
Plutonium is the only one of these transuranic elements that can exist a fair amount of time before radioactively decaying into lighter elements. — James Kaler

Examples of radioactive in a Sentence

Uranium and plutonium are radioactive.
Recent Examples on the Web Those include tax reform, the State budget, the radioactive pension reform crisis, and more., 17 Jan. 2022 In 2005, radioactive dating study pushed back the age of the fossil skull significantly, to 195,000 years ago. Brian Handwerk, Smithsonian Magazine, 12 Jan. 2022 On the Moon, this material also contains higher concentrations of radioactive isotopes, which will keep it warm for much longer, powering the extended period of volcanism that created the mare. John Timmer, Ars Technica, 11 Jan. 2022 China is now building the first molten-salt reactor that uses thorium as fuel, instead of more radioactive plutonium or uranium. Gernot Wagner, WSJ, 7 Jan. 2022 If the universe can bear up under the weight of so many movie remakes of various Peter Parkers being bitten by slightly different radioactive spiders, there’s space enough for a few more good biographies. Sam Negus, National Review, 6 Jan. 2022 First, there are the optimistic expectations raised by alternatives to the design of the 93 reactors currently in operation in the U.S. — reactors in which a radioactive core heats water, producing steam to drive electricity-generating turbines. Michael Hiltzik, Los Angeles Times, 6 Jan. 2022 Uranium prices jumped as Kazakhstan, the world’s largest producer of the radioactive metal, struggles to cope with deadly protests that pose the biggest challenge to the country’s leadership in decades. Fortune, 6 Jan. 2022 Because the equation doesn’t test kidney function directly, its developers compared its results with kidney filtration rates measured using a more definitive test, based on a radioactive tracer, that is too complex to perform routinely. Jyoti Madhusoodanan, Science | AAAS, 22 July 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'radioactive.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of radioactive

1898, in the meaning defined at sense 1

History and Etymology for radioactive

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Time Traveler for radioactive

Time Traveler

The first known use of radioactive was in 1898

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Dictionary Entries Near radioactive



radioactive chain

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Last Updated

20 Jan 2022

Cite this Entry

“Radioactive.” Dictionary, Merriam-Webster, Accessed 24 Jan. 2022.

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More Definitions for radioactive



English Language Learners Definition of radioactive

: having or producing a powerful and dangerous form of energy (called radiation)


ra·​dio·​ac·​tive | \ ˌrā-dē-ō-ˈak-tiv How to pronounce radioactive (audio) \

Kids Definition of radioactive

: caused by or exhibiting radioactivity a radioactive element


ra·​dio·​ac·​tive | \ ˌrād-ē-ō-ˈak-tiv How to pronounce radioactive (audio) \

Medical Definition of radioactive

: of, caused by, or exhibiting radioactivity radioactive isotopes

Other Words from radioactive

radioactively adverb

More from Merriam-Webster on radioactive

Nglish: Translation of radioactive for Spanish Speakers

Britannica English: Translation of radioactive for Arabic Speakers


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