Origin: Latin suffix -ive
Radioactive has 3 different meanings across 1 category:
Any radioactive substance.
"The contaminated soil became highly radioactive after the nuclear accident."
In plain English: A radioactive thing is an unstable material that naturally gives off energy and particles until it becomes safe.
"The doctors warned us to avoid any contact with radioactive waste from the factory."
exhibiting or caused by radioactivity
"radioactive isotope"
"radioactive decay"
"radioactive fallout"
Exhibiting radioactivity.
"The discarded medical equipment was found to be radioactive and had to be disposed of in a special shielded container."
Coined by Pierre Curie and Marie Curie in 1898 as French radio-actif, equivalent to English radio- + active.