Webster's English Dictionary

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radiation

ra.di.a.tion \.ra-d-e--'a--sh*n\ \-shn*l, -sh*n-*l\ \'ra-d-e--.a-t-iv\ n 
   1a: the action or process of radiating  1b1: the process of emitting 
   radiant energy in the form of waves or particl es 1b2: the combined 
   processes of emission, transmission, and absorption of ra diant energy 2a: 
   something that is radiated  2b: energy radiated in the form of waves or 
   particles  3: radial arrangement  4: RADIATOR  - ra.di.a.tion.al aj