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Syllabification: ra·di·a·tion
Pronunciation: /ˌrādēˈāSH(ə)n

Definition of radiation in English:


1 Physics The emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.
Example sentences
  • Because it uses sound waves instead of radiation, ultrasound is safer than X-rays.
  • When taken up by obstacles, beta particles produce a more penetrative secondary radiation known as bremsstrahlung.
  • We now know that invisible forces do control some things: gravity, radiation, electricity.
1.1The energy transmitted by radiation, as heat, light, electricity, etc.
Example sentences
  • The total spectrum of solar radiation comprises ultraviolet radiations, visible light, and infra-red radiations, in order of increasing electromagnetic wavelengths.
  • A radioactive source will emit these radiations at various frequencies, depending on its activity and its decay mode.
  • This foil doesn't do very well in the air, but it protected it from meteorites and from the ultraviolet radiations from the sun.
2chiefly Biology Divergence out from a central point, in particular evolution from an ancestral animal or plant group into a variety of new forms.
Example sentences
  • Each of these pulses is a major evolutionary radiation of the Theropsid lineage.
  • This famous site in British Columbia has yielded much fundamental information on the early radiation of the major animal groups.
  • During the Oligocene, the South American rodents began their great evolutionary radiation.


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



Pronunciation: /-ˈāSHənl/
Example sentences
  • On level sites, radiational cooling rather than cold air drainage is most significant in generating the ‘frost pocket’ phenomenon.
  • As it stagnates, with the days as long as they are, and the short nights, we don't have the radiational cooling and it just goes on and on.
  • When this cloud is present, night-time radiational cooling is much reduced and widespread fog is consequently not usually a problem.


Pronunciation: /-ˈāSHənl-ē/

Definition of radiation in:

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