/i ray'dee ay"sheuhn/ , n.
1. the act of irradiating.
2. the state of being irradiated.
3. intellectual or spiritual enlightenment.
4. a ray of light; beam.
5. Optics. the apparent enlargement of an object when seen against a dark background.
6. the use of x-rays or other forms of radiation for the treatment of disease, the making of x-ray photographs, the manufacture of vitamin D, etc.
7. exposure or the process of exposure to x-rays or other radiation.
8. Physics. irradiance.
[ 1580-90; irradiation- (s. of irradiatio ). See IR- 1 , RADIATION ]