From HomoExcelsior

1. Emission and propagation of energy in the form of rays or waves.
2. Energy radiated or transmitted in the form of rays, waves, or particles.
3. A stream of particles or electromagnetic waves emitted by the atoms and molecules of a radioactive substance as a result of nuclear decay.
4. Radial arrangement of parts, as of a group of nerve fibers connecting different areas of the brain.
5. The spread of a group of organisms into new habitats.
6. Adaptive radiation.