radiation

noun

ra·​di·​a·​tion ˌrā-dē-ˈā-shən 

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 

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

Recent Examples on the Web

The payloads are from Germany, South Korea, Saudi Arabia and Argentina and will study various impacts of space radiation on space hardware, monitor space weather, and how the environment affects electrical hardware bound for the moon. —Brendan Byrne, NPR, 2 Apr. 2026

The process is lengthy, and risks exposing people to radiation, which is why engineers hope robots can come to the rescue. —Katherine Bourzac, IEEE Spectrum, 2 Apr. 2026

Sanyuan Aerospace highlighted that the cable drive places drive control components inside the satellite body, which simplifies thermal control and radiation protection and reduces research and development costs. —Neetika Walter, Interesting Engineering, 1 Apr. 2026

To look at the leftover glow from the Big Bang, at the spectrum of temperature fluctuations (and also at the polarization) imprinted when neutral atoms first formed and the Universe became transparent to radiation. —Big Think, 1 Apr. 2026

Word History

First Known Use

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

Phrases Containing radiation

• adaptive radiation
• anti-radiation
• background radiation
• Cerenkov radiation
• cosmic background radiation
• electromagnetic radiation
• gamma radiation
• gravitational radiation
• radiation sickness
• radiation therapy
• secondary radiation
• synchrotron radiation
• X-radiation

Rhymes for radiation

• abdication
• aberration
• abjuration
• abnegation
• abrogation
• acceptation
• acclamation
• acclimation
• accusation
• activation
• actuation
• acylation

Kids Definition

radiation

noun

ra·​di·​a·​tion ˌrād-ē-ˈā-shən 

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 

-shən-ᵊl

adjective

Medical Definition

radiation

noun

ra·​di·​a·​tion ˌrād-ē-ˈā-shən 

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