radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty ˌrā-dē-ō-ak-ˈti-və-tē How to pronounce radioactivity (audio)
: the property possessed by some elements (such as uranium) or isotopes (such as carbon 14) of spontaneously emitting energetic particles (such as electrons or alpha particles) by the disintegration of their atomic nuclei
also : the rays emitted

Examples of radioactivity in a Sentence

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.
Still, traces of background radioactivity sometimes break the subterranean silence, with that activity piercing through LZ’s mile of protective bedrock or even seeping out of the materials lining the detector’s walls. — Joseph Howlett, Scientific American, 1 Sep. 2026 Scientists have conducted dives to collect samples and test the region to determine the extent of the pollution and whether the radioactivity has made its way into the food web. — Devika Rao, TheWeek, 31 Aug. 2026 When reactors burn transuranic elements in a fast neutron spectrum, the remaining waste loses its high radioactivity much faster. — Aman Tripathi, Interesting Engineering, 7 Aug. 2026 Shortly thereafter, a spike in radioactivity was detected nearby. — Geoff Brumfiel, NPR, 18 June 2026 See All Example Sentences for radioactivity

Word History

Etymology

International Scientific Vocabulary

First Known Use

1899, in the meaning defined above

Time Traveler
The first known use of radioactivity was in 1899

Rhymes for radioactivity

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Browse Nearby Words

radioactive series
radioactivity
radioallergosorbent
See all Nearby Words

Cite this Entry

“Radioactivity.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radioactivity. Accessed 2 Sep. 2026.

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Kids Definition

radioactivity

noun
ra·​dio·​ac·​tiv·​i·​ty -ˌak-ˈtiv-ət-ē How to pronounce radioactivity (audio)
: the giving off of rays of energy or particles by the breaking apart of atoms of certain elements (as uranium)

Medical Definition

radioactivity

noun
ra·​dio·​ac·​tiv·​i·​ty -ak-ˈtiv-ət-ē How to pronounce radioactivity (audio)
plural radioactivities
: the property possessed by some elements (as uranium) or isotopes (as carbon 14) of spontaneously emitting energetic particles (as electrons or alpha particles) by the disintegration of their atomic nuclei

More from Merriam-Webster on radioactivity

Britannica.com: Encyclopedia article about radioactivity

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