| a. | 1. | (Physics) Capable of luminescence under the action of cathode rays, X rays, or any of the allied forms of radiation. |
| 2. | (Physics) of, exhibiting, or caused by radioactivity. |
| Adj. | 1. | radioactive - exhibiting or caused by radioactivity; "radioactive isotope"; "radioactive decay"; "radioactive fallout" Antonyms: nonradioactive - not radioactive |