[ rey-dee-ey-shuhn ]
See synonyms for radiation on Thesaurus.com
  1. Physics.

    • the process in which energy is emitted as particles or waves.

    • the complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.

    • the energy transferred by these processes.

  2. the act or process of radiating.

  1. something that is radiated.

  2. radial arrangement of parts.

Origin of radiation

First recorded in 1545–55; from Latin radiātiōn-, stem of radiātiō “beam, gleam, shine”; equivalent to radiate + -ion

Other words from radiation

  • ra·di·a·tion·al, adjective
  • an·ti·ra·di·a·tion, adjective
  • in·ter·ra·di·a·tion, noun
  • non·ra·di·a·tion, noun

Words Nearby radiation

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use radiation in a sentence

British Dictionary definitions for radiation


/ (ˌreɪdɪˈeɪʃən) /

  1. physics

    • the emission or transfer of radiant energy as particles, electromagnetic waves, sound, etc

    • the particles, etc, emitted, esp the particles and gamma rays emitted in nuclear decay

  2. Also called: radiation therapy med treatment using a radioactive substance

  1. anatomy a group of nerve fibres that diverge from their common source

  2. the act, state, or process of radiating or being radiated

  3. surveying the fixing of points around a central plane table by using an alidade and measuring tape

Derived forms of radiation

  • radiational, adjective

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for radiation


[ rā′dē-āshən ]

    • Streams of photons, electrons, small nuclei, or other particles. Radiation is given off by a wide variety of processes, such as thermal activity, nuclear reactions (as in fission), and by radioactive decay.

    • The emission or movement of such particles through space or a medium, such as air. See Notes at conduction electromagnetic radiation.

  1. The use of such energy, especially x-rays, in medical diagnosis and treatment.

The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for radiation


The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.