Pronunciation: (rā"dē-ā'shun),[key] —n. 1. Physics. a. the process in which energy is emitted as particles or waves.
b. the complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.
c. the energy transferred by these processes.
2. the act or process of radiating.
3. something that is radiated.
4. radial arrangement of parts.