ra·di·a·tion | \ˌrā-dē-ˈā-shən \

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, -shə-nᵊl \ adjective
radiationless \ˌrā-dē-ˈā-shən-ləs \ adjective
radiative \ˈrā-dē-ˌā-tiv \ 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

The senator, 81, underwent chemotherapy and radiation treatment last summer, and has remained in Arizona for the past seven months. Yvonne Wingett Sanchez, azcentral, "A year after John McCain's cancer diagnosis, Cindy McCain expresses gratitude to caregivers," 13 July 2018 Debra Puffer, a 61-year-old resident of Rome, N.Y., was diagnosed with glioblastoma in 2014 and was treated with surgery, chemo, and radiation. Washington Post, BostonGlobe.com, "Polio virus treatment increased survival in patients with deadly brain tumors, study shows," 26 June 2018 But only some of their energy is channeled into such radiation, making supernovae somewhat inefficient killers. Adam Mann, Science | AAAS, "Dark energy’s weakness may be why supernovae didn’t kill us all," 4 May 2018 But black holes produce their own radiation, especially high-energy X-rays and gamma-rays, which shoot out from the star in the form of tightly collimated... Newsweek, "Analysis," 14 Mar. 2018 Cued by IceCube, the Antarctic detector, the orbiting Fermi Gammaray Space Telescope found that the neutrino likely came from a far off blazar, a hugely bright source of radiation powered by a supermassive black hole. Daniel Clery, Science | AAAS, "Ghostly particle caught in polar ice ushers in new way to look at the universe," 12 July 2018 These unusual subatomic particles are almost impossible to detect because they usually are unaffected by normal matter, radiation or gravity. Robert Lee Hotz, WSJ, "Scientists Track Neutrinos Through Ice to Their Source in the Cosmos," 12 July 2018 Chemo and radiation followed, and de Castro worked remotely while flying back and forth between New York and L.A. for several months. Colleen Leahey Mckeegan, Marie Claire, "The Business of Feeling Good," 11 July 2018 Genomic changes typically arise from rare errors during cell replication, or from exposure to carcinogens or radiation. Robert Martone, Scientific American, "Early Life Experience: It’s in Your DNA," 10 July 2018

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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Statistics for radiation

Last Updated

8 Oct 2018

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Time Traveler for radiation

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

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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 \

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 \

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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Comments on radiation

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one that holds something together

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