(ˌ)i, ə+ noun
( -s )
Etymology: Middle French, from Late Latin irradiation-, irradiatio, from Latin irradiatus + -ion-, -io -ion
1.
a. archaic : a giving off of rays of light
b. : the emission of radiant energy (as heat)
c. : an emanation, diffusion, or radiation of something from a common center or point of origin or a result of such activity: as
(1) : the radiation of a physiologically active agent from a point of origin within the body ; especially : the spread of a nervous impulse beyond the usual conduction path
(2) obsolete : emission of a supposed influence or immaterial fluid from the eyes
(3) : apparent enlargement of a light or bright object or surface when displayed against a dark background ; especially : the spreading of light by the grains of a photographic emulsion causing the developed image to be larger and more diffuse at the edges than the optical image — called also diffusion
2.
a. archaic : a ray of light
b. : mental or spiritual illumination
3.
a. : exposure to rays (as ultraviolet light, X rays, or alpha rays)
b. : application of X rays, radium rays, or other radiation (as for therapeutic purposes)
4. : irradiance 3