What does "radioactivity" mean?

Spontaneous emission of ionizing radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus.

How do you pronounce "radioactivity"?

Pronounced //ˌreɪdɪəʊakˈtɪvɪti//.

Common synonyms include: radiation, activity, artificial radioactivity, contamination, curiage, decay.

//ˌreɪdɪəʊakˈtɪvɪti// noun

noun ·Uncommon ·Advanced level

Noun

1
Spontaneous emission of ionizing radiation as a consequence of a nuclear reaction, or directly from the breakdown of an unstable nucleus. uncountable, usually
"Today, no one would intentionally smear radioactive materials on their face, but in 1933, the dangers of radioactivity were not yet fully understood."
2
the spontaneous emission of a stream of particles or electromagnetic rays in nuclear decay wordnet
3
The radiation so emitted; including gamma rays, alpha particles, neutrons, electrons, positrons, etc. uncountable, usually