n.1 the act or an instance of radiating; the process of being radiated.
2 Physics a the emission of energy as electromagnetic waves or as moving particles. b the energy transmitted in this way, esp. invisibly.
3 (in full radiation therapy) treatment of cancer and other diseases using radiation, such as X-rays or ultraviolet light.
Phrases and idioms:
radiation chemistry the study of the chemical effects of radiation on matter. radiation sickness sickness caused by exposure to radiation, such as X-rays or gamma rays.
radiational adj. radiationally adv.
Etymology: L radiatio (as RADIATE)