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mid-15c., "act or process of radiating," from Middle French radiation and directly from Latin radiationem (nominative radiatio) "a shining, radiation," noun of action from past participle stem of radiare "to beam, shine, gleam; make beaming," from radius "beam of light; spoke of a wheel" (see radius). Meaning "rays or beams emitted" is from 1560s. Meaning "divergence from a center" is 1650s.
radiation ra·di·a·tion (rā'dē-ā'shən)
The act or condition of diverging in all directions from a center.
The emission and propagation of energy in the form of rays or waves.
The energy radiated or transmitted in the form of rays, waves, or particles.
A stream of particles or electromagnetic waves that is emitted by the atoms and molecules of a radioactive substance as a result of nuclear decay.
The radial arrangement of anatomical or histological parts.
The spread of a group of organisms into new habitats.