Radiation \Ra`di*a"tion\, n. [L. radiatio: cf. F. radiation.]

1. The act of radiating, or the state of being radiated; emission and diffusion of rays of light; beamy brightness.

2. The shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat.

Source: Webster's Revised Unabridged Dictionary (1913)