ra·​di·​a·​tion | \ ˌrā-dē-ˈā-shən How to pronounce radiation (audio) \

Definition of radiation

1a : the action or process of radiating
b : the process of emitting radiant energy in the form of waves or particles
c(1) : the combined processes of emission, transmission, and absorption of radiant energy
(2) : the transfer of heat by radiation — compare conduction, convection
2a : something that is radiated
b : energy radiated in the form of waves or particles
3 : radial arrangement

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Other Words from radiation

radiational \ ˌrā-​dē-​ˈā-​shnəl How to pronounce radiational (audio) , -​shə-​nᵊl \ adjective
radiationless \ ˌrā-​dē-​ˈā-​shən-​ləs How to pronounce radiationless (audio) \ adjective
radiative \ ˈrā-​dē-​ˌā-​tiv How to pronounce radiative (audio) \ adjective

Examples of radiation in a Sentence

She was exposed to high levels of radiation. He goes in for radiation next week. the sun's radiation of heat
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Recent Examples on the Web Catherine Clawson underwent chemotherapy and radiation treatments for breast cancer three years ago. Chris Bumbaca, USA TODAY, "Wake Forest coach Dave Clawson will isolate from wife, Catherine, for entire football season," 26 June 2020 Most cited the potential, however small, of the Great Lakes — the drinking water source for more than 40 million people on both the U.S. and Canadian sides — becoming contaminated with radiation. Keith Matheny, Detroit Free Press, "Canadian utility formally drops underground radioactive waste storage next to Lake Huron," 24 June 2020 While undergoing chemotherapy and radiation, Arielle researched how food can affect health. Hannah Kirby, Milwaukee Journal Sentinel, "Last year, a Milwaukee couple started a vegan comfort food trailer. Now they've turned it into a Cudahy restaurant.," 19 June 2020 During the daytime, ultraviolet radiation from sunlight also inactivates any viral particles carried inside them, a process that takes a few minutes. Megan Molteni, Wired, "What Minnesota’s Protests Are Revealing About Covid-19 Spread," 18 June 2020 Rats not exposed to radiation were used as controls. Troy Farah, Ars Technica, "Vicodin, ketamine, and caffeine: The ingredients of a good space pharmacy," 8 June 2020 Those areas aren’t as high in radiation, but the exposure will leave whoever does that job puking for a few days. Dalene Rovenstine, EW.com, "The 100 recap: Russell Prime’s fate hangs in the balance," 4 June 2020 In brief, the geometry dictates that 100% of the radiation originating from the blackbody at A will land on and be absorbed by the blackbody at B because both A and B are the foci of ellipses E1 and E2. Quanta Magazine, "Why Our Perpetual Energy Puzzle Fails," 22 May 2020 Planets there might enjoy balmy temperatures, but the nearby star would also douse them with ultraviolet radiation and solar flares that could strip atmospheres and fry emerging microbes. Charlie Wood, Popular Science, "We’re one step closer to tracking down another Earth," 28 Aug. 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'radiation.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of radiation

15th century, in the meaning defined at sense 1a

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Time Traveler for radiation

Time Traveler

The first known use of radiation was in the 15th century

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Statistics for radiation

Last Updated

29 Jun 2020

Cite this Entry

“Radiation.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radiation. Accessed 3 Jul. 2020.

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More Definitions for radiation


How to pronounce radiation (audio)

English Language Learners Definition of radiation

: a type of dangerous and powerful energy that is produced by radioactive substances and nuclear reactions
medical : the use of controlled amounts of radiation for the treatment of diseases (such as cancer)
: energy that comes from a source in the form of waves or rays you cannot see


ra·​di·​a·​tion | \ ˌrā-dē-ˈā-shən How to pronounce radiation (audio) \

Kids Definition of radiation

1 : the process of giving off energy in the form of waves or particles
2 : something that is radiated (as light or X-rays)


ra·​di·​a·​tion | \ ˌrād-ē-ˈā-shən How to pronounce radiation (audio) \

Medical Definition of radiation

1 : energy radiated in the form of waves or particles
2a : the action or process of radiating with radiation of the pain there may be tenderness over the sciatic nerve— J. A. Key
b(1) : the process of emitting radiant energy in the form of waves or particles
(2) : the combined processes of emission, transmission, and absorption of radiant energy
3 : a tract of nerve fibers within the brain especially : one concerned with the distribution of impulses arising from sensory stimuli to the relevant coordinating centers and nuclei the optic radiations

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More from Merriam-Webster on radiation

Rhyming Dictionary: Words that rhyme with radiation

Spanish Central: Translation of radiation

Nglish: Translation of radiation for Spanish Speakers

Britannica English: Translation of radiation for Arabic Speakers

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