n.
1.the condition of being exposed to radiation
2.a column of light (as from a beacon)
3.(physiology) the spread of sensory neural impulses in the cortex
4.the apparent enlargement of a bright object when viewed against a dark background
5.(Pavolvian conditioning) the elicitation of a conditioned response by stimulation similar but not identical to the original stimulus
6.(medicine) the treatment of disease (especially cancer) by exposure to radiation from a radioactive substance