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

The agency’s radioactivity with the gun-rights lobby has left it on shaky political ground. — Alec MacGillis, ProPublica, 1 June 2026

If correct, that meant that something strange was going on with the particles governing radioactivity and with the rules of physics. — Clara Moskowitz, Scientific American, 10 Apr. 2026

Then, that soil will be tested for radioactivity, wrapped in special packaging and stored in heavy-metal containers. — Andy Sheehan, CBS News, 14 Apr. 2026

Shortly thereafter, a spike in radioactivity was detected nearby. — Geoff Brumfiel, NPR, 18 June 2026

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