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

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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 Luckily for humans, the radioactive decay of cesium-137 has reduced the levels of the isotope in the environment since the weapons tests. Alex Fox, Smithsonian Magazine, "Fallout From Cold War Nuclear Testing Detected in U.S. Honey," 24 Apr. 2021 Discharging waste water into the sea is a common practice, once the water has been treated to remove most radioactive elements. Eamon Barrett, Fortune, "After cutting Jack Ma down to size, who will Beijing target next?," 13 Apr. 2021 Uranium mining is a deeply polarizing issue in Greenland, whose 1988 ban on extracting radioactive materials was only lifted in 2014 by a single vote in parliament. Drew Hinshaw, WSJ, "China’s Rare-Earths Quest Upends Greenland’s Government," 7 Apr. 2021 Though officials have said that the water leaking out of the facility is not radioactive, there is still concern about its chemical content. Li Cohen, CBS News, "Floridians evacuated from Piney Point area can now return home — but the reservoir is still leaking," 7 Apr. 2021 State authorities say the water in the breached pond is not radioactive. Fox News, "Florida Piney Point wastewater reservoir does not have a second breach, officials say," 6 Apr. 2021 Micro-sized single crystal diamonds move heat away from the radioactive isotope materials so quickly that the transaction generates electricity. Caroline Delbert, Popular Mechanics, "The Radioactive Diamond Battery That Will Run For 28,000 Years," 30 Mar. 2021 Off-site releases of radioactive materials contaminated land in Fukushima and several neighboring prefectures. Popular Science, "10 years after Fukushima, outdated nuclear power plants are still the norm," 11 Mar. 2021 Barrels of industrial trash, radioactive materials, oil refinery waste, rotting meats and various acid sludges also got dumped into the sea. Rosanna Xia, Star Tribune, "Sea lions are dying from a mysterious cancer. The culprits? Herpes and DDT," 11 Mar. 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

International Scientific Vocabulary

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Time Traveler for radioactive

Time Traveler

The first known use of radioactive was in 1898

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Statistics for radioactive

Last Updated

26 Apr 2021

Cite this Entry

“Radioactive.” Dictionary, Merriam-Webster, Accessed 7 May. 2021.

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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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