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

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 Overexposure to benzenes, toluene, herbicides, pesticides, organic solvents, painting materials and lead might contribute to low sperm counts and exposure to x-rays or other radiation might alter sperm production, according to the Mayo Clinic. Mari A. Schaefer, Philly.com, "Study: Nutrition in nuts may help boost sperm count," 10 July 2018 For their mouse research, Kirkland and his team first transplanted half a million Methuselah cells (made ultra-old with drugs or radiation) into young (6 months old) or middle-aged (17 months old) mice. Sharon Begley, STAT, "Hope for creaky old humans: removing aged cells from mice can restore their youth, study finds," 9 July 2018 The exact treatment plan for non-Hodgkin's lymphoma depends on the type and location of the cancer but may include a combination of surgery, chemotherapy, immunotherapy, and radiation. Andrea Park, SELF, "After a Second Back Surgery, Abby Lee Miller Shows Off Her Healing Progress on Instagram," 2 July 2018 The Berkeley law, in effect since 2016, tells dealers to notify their customers that the federal government sets radiation standards for cell phones. Bob Egelko, SFChronicle.com, "U.S. Supreme Court ruling raises questions about Berkeley cell phone ordinance," 28 June 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

10 Sep 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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the setting in which something occurs

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