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 radiation (audio) , -​shə-​nᵊl \ adjective
radiationless \ ˌrā-​dē-​ˈā-​shən-​ləs How to pronounce radiation (audio) \ adjective
radiative \ ˈrā-​dē-​ˌā-​tiv How to pronounce radiation (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 During the Cold War, Washington feared that Moscow was turning microwave radiation into a covert weapon that could produce neural impact. Néstor T. Carbonell, National Review, "The Havana Syndrome: Unraveling the Mystery," 11 May 2021 Pavon continued to teach her fourth-grade class despite side effects such as radiation burns and fatigue. Laura Garcia, San Antonio Express-News, "'It all caught up to me': San Antonio researcher to study life after cancer for Latinos," 10 May 2021 But at the same time, the baby absorbed that radiation from her. Dalton Ross, EW.com, "Fear the Walking Dead showrunners explain that devastating twist ending," 10 May 2021 She was diagnosed in August of 2019 and has worked while taking radiation, chemo infusion and now oral chemo. Kyle Neddenriep, The Indianapolis Star, "IndyStar's Sports Mom of the Year 'has been a mother to many more than just her own boys.'," 8 May 2021 However, the quantum vacuum itself will exhibit real, physical effects on matter and radiation that passes through them. Ethan Siegel, Forbes, "Ask Ethan: Do Virtual Particles Really Exist?," 7 May 2021 Greenhouse gases accumulate in the atmosphere like a blanket, trapping radiation that would otherwise escape into space. Laura Smith-spark And Ivana Kottasová, CNN, "China's annual emissions surpass those of all developed nations combined, report finds," 7 May 2021 Researchers conducting the experiment sent the case of Bordeaux to study how space, with differing levels of gravity and radiation than on Earth, would affect the wines' aging. Ryan W. Miller, USA TODAY, "Space wine: Bottle of Bordeaux that spent more than a year in orbit up for sale for reported $1 million," 5 May 2021 Ultraviolet radiation can damage proteins and DNA in human cells, and this results in sunburns and can cause cancer. R. O. Parke Loyd, The Conversation, "Massive flare seen on the closest star to the solar system: What it means for chances of alien neighbors," 3 May 2021

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

13 May 2021

Cite this Entry

“Radiation.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radiation. Accessed 18 May. 2021.

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More Definitions for radiation



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

More from Merriam-Webster on radiation

Nglish: Translation of radiation for Spanish Speakers

Britannica English: Translation of radiation for Arabic Speakers

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