Definition of radiation in US English:



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

    • ‘Because it uses sound waves instead of radiation, ultrasound is safer than X-rays.’
    • ‘Huygens stated that an expanding sphere of light behaves as if each point on the wave front were a new source of radiation of the same frequency and phase.’
    • ‘When taken up by obstacles, beta particles produce a more penetrative secondary radiation known as bremsstrahlung.’
    • ‘The board does say that there is still a need for further research into other concerns over the safety of microwave radiation.’
    • ‘We now know that invisible forces do control some things: gravity, radiation, electricity.’
    discharge, release, outpouring, outflow, outrush, leak, excretion, secretion, ejection
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    1. 1.1 The energy transmitted by radiation, as heat, light, electricity, etc.
      • ‘It is these materials that emit gamma rays, high energy radiation that can pass right through your skin.’
      • ‘A radioactive source will emit these radiations at various frequencies, depending on its activity and its decay mode.’
      • ‘The total spectrum of solar radiation comprises ultraviolet radiations, visible light, and infra-red radiations, in order of increasing electromagnetic wavelengths.’
      • ‘Radioactivity is the process of emission of radiation as a radioactive material changes form, often to a different element.’
      • ‘This foil doesn't do very well in the air, but it protected it from meteorites and from the ultraviolet radiations from the sun.’
      transference, transferral, passing on, communication, conveyance, imparting, channelling, carrying, relaying, dispatch, mediation
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  • 2Biology
    Divergence out from a central point, in particular evolution from an ancestral animal or plant group into a variety of new forms.

    • ‘The radiation of modern felines began with the divergence of the Panthera lineage.’
    • ‘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.’
    • ‘Rate variation among lineages is the footprint of selection and can be indicative of species radiations or differential structural constraints.’


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