Radioactively describes something happening in a way that involves or relates to radioactivity, which is when certain atoms become unstable and release invisible energy and particles. When scientists say a material behaves radioactively, they mean it's emitting this special kind of energy, not that it's necessarily glowing with visible light.

Uranium and plutonium decay radioactively over thousands of years, steadily releasing energy as their atoms break apart. This process powers nuclear reactors and once powered certain types of spacecraft. Marie Curie studied materials that behaved radioactively, like radium, though people at the time didn't yet understand the health dangers of working so closely with radioactive materials.

The word can also be used figuratively to mean something is intensely powerful or dangerous, like when someone describes a controversial topic as radioactively sensitive, meaning people react to it with extreme caution or strong emotions. A journalist might avoid investigating something radioactively controversial because touching it could damage their career.

In science fiction, characters sometimes gain superpowers from radioactively contaminated spiders or other sources, though real radioactivity doesn't work that way. It's dangerous rather than magical, which is why radioactive materials require careful handling and special protective equipment.