ra·​dio·​ac·​tive | \ ˌrā-dē-ō-ˈak-tiv \

Definition of radioactive

: of, caused by, or exhibiting radioactivity

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Other Words from radioactive

radioactively adverb

Examples of radioactive in a Sentence

Uranium and plutonium are radioactive.

Recent Examples on the Web

Here’s how The subject of this description is radiometric dating, which uses radioactive decay of some elements to figure out how old things are. John Timmer, Ars Technica, "Video: How do we figure out that rocks are billions of years old?," 30 Oct. 2018 Sediment core samples taken from ancient seabeds show a huge spike in radioactive particles right around the time when the megalodon disappeared. Jill Kiedaisch, Popular Mechanics, "Exploding Stars Might Have Brought an End to the Prehistoric Megalodon," 14 Dec. 2018 While no detonation happened, it was later revealed that the site was radioactively contaminated by another secret experiment in which the government buried several thousand pounds of radioactive soil in the same area without telling nearby people. Maka Monture, Teen Vogue, "10 Films That Show How the U.S. Has Mistreated Native Americans and Alaska Natives," 22 Nov. 2018 Burning coal to produce energy leaves behind ash, which contains toxic heavy metals and radioactive material, substances that can lead to cancer and neurological damage. Umair Irfan, Vox, "Florence dropped so much rain that hog waste is spilling out of lagoons," 18 Sep. 2018 Additionally, about 1,000 tons of radioactive scrap metal was shipped to the Luckey site in the early 1950s, in anticipation of converting the plant back to its original magnesium processing activities. Keith Matheny, Detroit Free Press, "Radioactive soil from Ohio heads to Wayne County landfill next week," 22 June 2018 Any nuclear deal will hinge on North Korea's willingness to allow unfettered outside inspections of the country's warheads and radioactive materials, much of which is likely kept in a vast complex of underground facilities. Fox News, "Kim Jong Un arrives in Singapore for summit with Trump," 10 June 2018 The radioactive metal is considered the founding step for aggressive programs set on making a variety of nuclear arms. New York Times, "North Korea Nuclear Disarmament Could Take 15 Years, Expert Warns," 28 May 2018 And certainly nobody told them that they had been showered with the radioactive metal after a fire there. Fred Pearce, Time, "How the 'Compulsive Secrecy’ of the Atomic Age Has Changed the Way We Think," 22 May 2018

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 above

History and Etymology for radioactive

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Last Updated

18 Jan 2019

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Time Traveler for radioactive

The first known use of radioactive was in 1898

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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 \

Kids Definition of radioactive

: caused by or exhibiting radioactivity a radioactive element


ra·​dio·​ac·​tive | \ ˌrād-ē-ō-ˈak-tiv \

Medical Definition of radioactive

: of, caused by, or exhibiting radioactivity radioactive isotopes

Other Words from radioactive

radioactively adverb

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More from Merriam-Webster on radioactive

Spanish Central: Translation of radioactive

Nglish: Translation of radioactive for Spanish Speakers

Britannica English: Translation of radioactive for Arabic Speakers

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a complex dispute or argument

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