/ ˌreɪdiˈeɪʃn; NAmE / noun
1.
[ U , C ] powerful and very dangerous rays that are sent out from radioactive substances :
high levels / doses of radiation that damage cells
the link between exposure to radiation and childhood cancer
a radiation leak from a nuclear power station
radiation sickness
the radiations emitted by radium
2.
[ U ] heat, energy, etc. that is sent out in the form of rays :
ultraviolet radiation
electromagnetic radiation from power lines
3.
(also ˌradiˈation therapy ) [ U ] the treatment of cancer and other diseases using radiation
—compare chemotherapy , radiotherapy
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WORD ORIGIN
late Middle English (denoting the action of sending out rays of light): from Latin radiatio(n-) , from radiare emit rays, from radius ray, spoke.