radiation — ODE

radiation /ˌreɪdiˈeɪʃn

▸ noun [mass noun]

1 Physics the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles which cause ionization.

▪ the energy transmitted by radiation:

background radiation

[as modifier] the radiation dose

[count noun] ultraviolet and infrared radiations.

2 mainly Biology divergence out from a central point, in particular evolution from an ancestral animal or plant group into a variety of new forms:

evolution is a process of radiation not progression.

– ORIGIN late Middle English (denoting the action of sending out rays of light): from Latin radiatio(n-), from radiare ‘emit rays’ (see radiate).