radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty ˌrā-dē-ō-ak-ˈti-və-tē 

: 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

Even Marie Curie, a pioneer in radioactivity research, which has been used to fight cancer, died after years of exposure to radiation through her work. —John F. McQuillan, Forbes, 21 Mar. 2025

Over the decades its radioactivity will gradually fade, along with the Japanese public’s memory of the accident. —IEEE Spectrum, 28 Feb. 2014

Second, most Germans have been soundly against nuclear energy ever since the 1986 Chernobyl meltdown in Ukraine lofted a cloud of airborne radioactivity over the country’s northern territory. —Paul Hockenos, Foreign Affairs, 26 Sep. 2013

Japan Agency for Marine-Earth Science and Technology plans to measure radioactivity around the plant from March 22 to March 23. —IEEE Spectrum, 15 Mar. 2011

Word History

Etymology

International Scientific Vocabulary

First Known Use

1899, in the meaning defined above

Rhymes for radioactivity

• bioactivity
• commutativity
• cooperativity
• generativity
• hyperactivity
• insensitivity
• interactivity
• overactivity
• performativity
• retroactivity
• absorptivity
• affectivity

Kids Definition

radioactivity

noun

ra·​dio·​ac·​tiv·​i·​ty -ˌak-ˈtiv-ət-ē 

: 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 

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