Definition of radiation in English:

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Pronunciation: /ˌrādēˈāSH(ə)n/


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.



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/


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

  • ray from Middle English:

    The ray that means ‘beam of light’ is a medieval word going back to Latin radius ‘spoke, ray’, the source of radiate (late 16th century) , radio (early 20th century), and radius (late 16th century). The term ray of sunshine for someone who brings happiness into the lives of others, dating back to the early 20th century, is often used ironically for someone who in fact spreads little cheer. Ray as a name for a fish is a different word, from Latin raia.

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Syllabification: ra·di·a·tion

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