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
: adaptive radiation
radiational
ˌrā-dē-ˈā-sh(ə-)nəl How to pronounce radiation (audio)
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
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.
In trials, radiation either shrank tumors or stopped them from growing, in all patients evaluated. — Sun Sentinel Editorial Board, Sun Sentinel, 31 Aug. 2026 Students will also study mines and explosive hazards, first aid for combat injuries, chemical and radiation exposure and acute stress, as well as survival training and procedures for operating in conflict zones. — Bloomberg, Fortune, 29 Aug. 2026 The Environmental Protection Agency has jurisdiction over certain radiation that goes beyond the site boundary of a nuclear facility. — Los Angeles Times, 28 Aug. 2026 The bamboo and wood fibers are modified to withstand conditions including high humidity, corrosion, salt spray, and ultraviolet radiation, according to professor Qi Chusheng, who spoke to China Green Times. — Neetika Walter, Interesting Engineering, 28 Aug. 2026 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

Phrases Containing radiation

Rhymes for radiation

See All Rhymes for radiation

Browse Nearby Words

radiateness
radiation
radiational
See all Nearby Words

Cite this Entry

“Radiation.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/radiation. Accessed 1 Sep. 2026.

Copy Citation

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 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
Last Updated: - Updated example sentences
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Popular in Grammar & Usage

See More

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

Is it 'nerve-racking' or 'nerve-wracking'?

What's the difference between 'fascism' and 'socialism'?

Why does English have so many silent letters?

7 Pairs of Commonly Confused Words
See More

Popular in Wordplay

See More

Ye Olde Nincompoop: Old-Fashioned Words for 'Stupid'

14 Phobias You Probably Haven't Heard Of

Even More Words That Sound Like Insults But Aren't

Even More Bird Names that Sound Like Insults (and Sometimes Are)

12 Lovely and Unusual Words for the Natural World
See More

Popular

See More

A Who’s Who Regarding ‘Who’s’ and ‘Whose’

Ye Olde Nincompoop: Old-Fashioned Words for 'Stupid'

14 Phobias You Probably Haven't Heard Of
See More

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
The Missing Letter A daily crossword with a twist
skateboard-dog-hat
Wordmaxxing Slang Quiz Give your vocabulary a glow up by getting sendy w...
See All