radioactive

The word “radioactive” means giving off radiation from the decay of unstable atomic nuclei. In plain terms, emitting radiation from unstable atoms, or figuratively, too toxic or controversial to touch.

“Radioactive” is pronounced ray-dee-oh-AKTIHV (/ˌɹeɪdioʊˈæktɪv/ in IPA).

Here is “radioactive” used in a sentence: “Radioactive waste must be stored safely for thousands of years.”

“Radioactive” is an adjective.

The word “radioactive” dates back to around 1898 and comes from French. Coined by Pierre and Marie Curie in 1898 as the French radio-actif, from "radio-" plus "active".

“Radioactive” is a fairly common word in modern English.

“Radioactive” has 2 distinct senses listed in this dictionary. The most common is: giving off radiation from the decay of unstable atomic nuclei.

Radioactive describes a material that gives off radiation from the decay of unstable atomic nuclei, while nuclear refers more broadly to anything involving atomic nuclei, including reactions that may not release radiation on their own. A substance can be nuclear-related without necessarily being radioactive.

A material becomes radioactive when it contains unstable atomic nuclei that break down, or decay, releasing energy in the form of radiation. This decay continues until the unstable atoms become stable.

Figuratively, calling a topic or person radioactive means it is so controversial or toxic that others avoid associating with it, much as people keep their distance from harmful radiation.