radiation

noun

ra·​di·​a·​tion ˌrā-dē-ˈā-shən How to pronounce radiation (audio)
1
a
: 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
2
a
: something that is radiated
b
: energy radiated in the form of waves or particles
3
: radial arrangement
4
radiational adjective
radiationless adjective
radiative 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
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Fifteen states will experience elevated ultraviolet (UV) radiation levels this weekend, according to the National Weather Service (NWS) and the Environmental Protection Agency (EPA). Joe Edwards, MSNBC Newsweek, 27 June 2025 Life on Earth has evolved to withstand two types of UV radiation: UVA rays (comprising the bulk of radiation that reaches Earth) and UVB rays (mostly absorbed by ozone in the atmosphere). Jack Knudson, Discover Magazine, 25 June 2025 Because of their curious ability to transmute into photons in the presence of strong magnetic fields, any place that features strong fields—think neutron stars or even the solar corona—could produce extra radiation due to axions. ArsTechnica, 25 June 2025 When the hairs on different spiderwort species are exposed to low radiation, the blooms may turn pink, according to several sources. Sheryl De Vore, Chicago Tribune, 23 June 2025 See All Example Sentences for radiation

Word History

First Known Use

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

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

Browse Nearby Words

Cite this Entry

“Radiation.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radiation. Accessed 4 Jul. 2025.

Kids Definition

radiation

noun
ra·​di·​a·​tion ˌrād-ē-ˈā-shən How to pronounce radiation (audio)
1
: the action or process of radiating
especially : the process of giving off radiant energy in the form of waves or particles
2
: something that is radiated
especially : energy radiated in the form of waves or particles
radiational
-shnəl How to pronounce radiation (audio)
-shən-ᵊl
adjective

Medical Definition

radiation

noun
ra·​di·​a·​tion ˌrād-ē-ˈā-shən How to pronounce radiation (audio)
1
: energy radiated in the form of waves or particles
2
a
: the action or process of radiating
with radiation of the pain there may be tenderness over the sciatic nerveJ. 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

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