radiation

American  

[rey-dee-ey-shuhn] / ˌreɪ diˈeɪ ʃən /

noun

1. Physics.

   1. the process in which energy is emitted as particles or waves.

   2. the complete process in which energy is emitted by one body, transmitted through an intervening medium or space, and absorbed by another body.

   3. the energy transferred by these processes.

2. the act or process of radiating.

3. something that is radiated.

4. radial arrangement of parts.

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radiation British  

/ ˌreɪdɪˈeɪʃən /

noun

1. physics

   1. the emission or transfer of radiant energy as particles, electromagnetic waves, sound, etc

   2. the particles, etc, emitted, esp the particles and gamma rays emitted in nuclear decay

2. Also called: radiation therapy.  med treatment using a radioactive substance

3. anatomy a group of nerve fibres that diverge from their common source

4. See adaptive radiation

5. the act, state, or process of radiating or being radiated

6. surveying the fixing of points around a central plane table by using an alidade and measuring tape

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radiation Scientific  

/ rā′dē-ā′shən /

1. 1. Streams of photons, electrons, small nuclei, or other particles. Radiation is given off by a wide variety of processes, such as thermal activity, nuclear reactions (as in fission), and by radioactive decay.

   2. The emission or movement of such particles through space or a medium, such as air.

2. The use of such energy, especially x-rays, in medical diagnosis and treatment.

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radiation Cultural  

1. Energy sent out in the form of particles or waves. (See alpha radiation, beta radiation, blackbody, cosmic rays, electromagnetic radiation, fluorescence, gamma radiation, photon, and quanta.)

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Other Word Forms

• antiradiation adjective
• interradiation noun
• nonradiation noun
• radiational adjective

Etymology

Origin of radiation

First recorded in 1545–55; from Latin radiātiōn-, stem of radiātiō “beam, gleam, shine”; equivalent to radiate + -ion

Explanation

Radiation is energy transmitted in waves or a stream of particles. The first thing you think of as radiation is probably X-rays, but what cooks your food in the microwave oven is also radiation. Radiation has some important medical uses, especially in the treatment of cancer, as "radiation therapy." It’s also associated with such horrors as "radiation sickness" — observed in people exposed to high levels of radiation, as in the aftermath of the 1986 explosion at the Chernobyl nuclear reactor, in the Ukraine. You can also use the word radiation, in more benign contexts, to describe something spreading out from a central point, as the radiation of warmth from your fireplace.

Example Sentences

In some models, when two of these particles meet, they annihilate and produce high-energy radiation such as gamma rays.

From Science Daily • Apr. 10, 2026

"Our prediction is that we'll see a lot more galactic cosmic radiation... which is from supernovas and is everywhere," versus radiation coming from the Sun, he said.

From Barron's • Apr. 10, 2026

"No increase in radiation levels was reported," it wrote on X.

From BBC • Apr. 4, 2026

Fuel shortages are keeping doctors and nurses away from work and hospitals are canceling surgeries and delaying vaccines for children and life-saving treatments such as kidney dialysis and radiation therapy.

From Los Angeles Times • Apr. 1, 2026

It provided a shield, preventing radiation from escaping, and it also cooled the rods.

From "Meltdown" by Deirdre Langeland

Related Words

• emission