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

Derived Forms

• nonradiation
  noun
• radiational
  adjective
• interradiation
  noun
• antiradiation
  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

Radiation levels at the facility remained within normal limits following the attack, although its fuel reception building was "partially destroyed", according to Ukraine's nuclear energy operator, Energoatom.

From Barron's • Jun. 7, 2026

Radiation on Mars, and the planet’s different disease burden, would speed up mutations there.

From The Wall Street Journal • Feb. 19, 2026

“This move is a fundamental betrayal of EPA’s responsibility to protect human health,” said Joseph Goffman, former assistant administrator of the EPA Office of Air and Radiation.

From Los Angeles Times • Feb. 12, 2026

Radiation levels will be higher than on the International Space Station, which is in low‑Earth orbit, but still safe.

From BBC • Jan. 9, 2026

Physicists at the Radiation Faboratory and elsewhere picked away at the secrets of uranium fission all that year, trying to answer Oppenheimer’s questions as well as others more fundamental.

From "Big Science" by Michael Hiltzik

Related Words

• emission