[ rey-dee-ey-shuhn ]
/ ˌreɪ diˈeɪ ʃən /
Save This Word!


  1. the process in which energy is emitted as particles or waves.
  2. the complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.
  3. the energy transferred by these processes.
the act or process of radiating.
something that is radiated.
radial arrangement of parts.



Apostrophes can be tricky; prove you know the difference between it’s and its in this crafty quiz!
Question 1 of 12
On the farm, the feed for chicks is significantly different from the roosters’; ______ not even comparable.

Origin of radiation

1545–55; <Latin radiātiōn- (stem of radiātiō) a glittering, shining. See radiate, -ion
ra·di·a·tion·al, adjectivean·ti·ra·di·a·tion, adjectivein·ter·ra·di·a·tion, nounnon·ra·di·a·tion, noun
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2021

British Dictionary definitions for radiation

/ (ˌreɪdɪˈeɪʃən) /


  1. the emission or transfer of radiant energy as particles, electromagnetic waves, sound, etc
  2. the particles, etc, emitted, esp the particles and gamma rays emitted in nuclear decay
Also called: radiation therapy med treatment using a radioactive substance
anatomy a group of nerve fibres that diverge from their common source
the act, state, or process of radiating or being radiated
surveying the fixing of points around a central plane table by using an alidade and measuring tape
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

Medical definitions for radiation

[ rā′dē-āshən ]


The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

Scientific definitions for radiation

[ rā′dē-āshən ]

  1. 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.
  2. The emission or movement of such particles through space or a medium, such as air. See Notes at conduction electromagnetic radiation.
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.
Hate Typos? Get Grammar Coach