radioactive

adjective

ra·​dio·​ac·​tive ˌrā-dē-ō-ˈak-tiv How to pronounce radioactive (audio)
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
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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Striking Iran's nuclear reactors -- used to generate nuclear power -- wouldn't release nearly as much radioactive material as Chernobyl, the experts said. Julia Jacobo, ABC News, 21 June 2025 There is also a chance that radioactive material could seep into any water source that’s running through the mountain. Alexander Smith, NBC news, 20 June 2025 Many groups are approaching the problem by trying to find a cost-effective way to shorten the lifespan of radioactive waste to tens or hundreds of years, through transmutation. IEEE Spectrum, 7 July 2025 The landfill's acceptance of toxic waste from a 2023 Ohio train derailment, and plans to take radioactive wastes from a World War II-era atomic bomb development facility in New York, have raised ire. Keith Matheny, Freep.com, 3 July 2025 See All Example Sentences for radioactive

Word History

Etymology

International Scientific Vocabulary

First Known Use

1898, in the meaning defined at sense 1

Time Traveler
The first known use of radioactive was in 1898

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Cite this Entry

“Radioactive.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radioactive. Accessed 14 Jul. 2025.

Kids Definition

radioactive

adjective
ra·​dio·​ac·​tive ˌrād-ē-ō-ˈak-tiv How to pronounce radioactive (audio)
: of, caused by, or exhibiting radioactivity
radioactively adverb

Medical Definition

radioactive

adjective
ra·​dio·​ac·​tive ˌrād-ē-ō-ˈak-tiv How to pronounce radioactive (audio)
: of, caused by, or exhibiting radioactivity
radioactive isotopes
radioactively adverb

More from Merriam-Webster on radioactive

Last Updated: - Updated example sentences
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