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

Molten salt will contain the isotopes to reduce risks associated with remaining radioactivity. —IEEE Spectrum, 7 July 2025

The danger isn't radioactivity but rather the heavy metals, Bernstein said. —Julia Jacobo, ABC News, 21 June 2025

So far, there are no elevated levels of radioactivity being reported, Emily A. Caffrey, director for the Health Physics Program at the University of Alabama at Birmingham, told ABC News. —Julia Jacobo, ABC News, 23 June 2025

Curie, the first woman to win a Nobel Prize, revolutionized science with her work on radioactivity. —Harry Booth / Paris, TIME, 6 Feb. 2025

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