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 Up until recently, the only way to test for Alzheimer's was to do a spinal tap or use an expensive brain scan that required injecting a radioactive tracer and is only performed at specialized centers. Sandee Lamotte, CNN, "Key 2020 health stories you may have missed because of Covid-19," 28 Dec. 2020 In the 1950s, many of these movies used alien invasions or radioactive creatures to explore Cold War fears. Kate Knibbs, Wired, "Can Disaster Movies Survive a Pandemic?," 25 Dec. 2020 Blazes at such sites could release toxins ranging from acid mine drainage to radioactive smoke. NBC News, "Wildfires fueled by climate change threaten toxic Superfund sites," 23 Dec. 2020 Two elements remain, cesium and strontium, that are dangerously radioactive for some 270 years. William Levin, National Review, "We Have Time to Prevent Climate Change," 15 Dec. 2020 Tritium is radioactive with a half-life of 12 years and global supplies are low. Daniel Clery, Science | AAAS, "U.K. seeks site for world’s first fusion power station," 2 Dec. 2020 Special air filters remove radioactive particles from air entering the aircraft, and the number of interior doors have been reduced. Kyle Mizokami, Popular Mechanics, "Thieves Break Into Russia’s Nuclear War 'Doomsday' Jet," 10 Dec. 2020 In recent years, the plant has come under intense scrutiny after it was found to be leaking radioactive water into the Biscayne Bay. Tim Mcdonnell, Quartz, "How wind and solar toppled Exxon from its place as America’s top energy company," 30 Nov. 2020 To see why, consider radioactive dating, a marvelous technique for determining the age of objects. Frank Wilczek, WSJ, "The Clock Paradox of Quantum Physics," 3 Dec. 2020

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

8 Jan 2021

Cite this Entry

“Radioactive.” Dictionary, Merriam-Webster, Accessed 16 Jan. 2021.

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More Definitions for radioactive


How to pronounce radioactive (audio)

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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