circadian
adjective
cir·ca·di·an
sər-ˈkā-dē-ən 
: being, having, characterized by, or occurring in approximately 24-hour periods or cycles (as of biological activity or function)
circadian rhythms in activity
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In 1959, a scientist formed the word circadian from the Latin words circa ("about") and dies ("day"), and it caught on quickly. Most often, it's seen and heard in the term circadian rhythm, which refers to the inherent cycle of about 24 hours that appears to control various biological processes, such as sleep, wakefulness, and digestive activity. If you want to impress your friends, you can also use the term circadian dysrhythmia, a fancy synonym of jet lag.
Examples of circadian in a Sentence
Recent Examples on the Web
The biannual time shift tends to affect peoples’ circadian rhythms — the body’s 24-hour clock — which regulate several physiological processes.
—
Hannah Poukish, Sacbee.com, 22 Oct. 2025
Your doom-scrolling brain will thank you for the circadian rhythm reset, and your groggy self will appreciate the thoughtful up-and-at-em assist.
—Julia Harrison, Architectural Digest, 21 Oct. 2025
And the exposure to bright artificial flashes of light, even for milliseconds, can not only disrupt human circadian rhythms, leading to less and lower-quality sleep, but has also been linked to certain types of cancers in humans.
—Big Think, 15 Oct. 2025
Adequate rest is crucial, Johnson said, because the brain’s process of clearing out toxins is thought to follow circadian rhythms and works best during sleep.
—The Washington Post, San Diego Union-Tribune, 14 Oct. 2025
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Hannah Poukish, Sacbee.com, 22 Oct. 2025
Your doom-scrolling brain will thank you for the circadian rhythm reset, and your groggy self will appreciate the thoughtful up-and-at-em assist.
—Julia Harrison, Architectural Digest, 21 Oct. 2025
And the exposure to bright artificial flashes of light, even for milliseconds, can not only disrupt human circadian rhythms, leading to less and lower-quality sleep, but has also been linked to certain types of cancers in humans.
—Big Think, 15 Oct. 2025
Adequate rest is crucial, Johnson said, because the brain’s process of clearing out toxins is thought to follow circadian rhythms and works best during sleep.
—The Washington Post, San Diego Union-Tribune, 14 Oct. 2025
See All Example Sentences for circadian
Cite this Entry
“Circadian.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/circadian. Accessed 24 Oct. 2025.
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circadian
adjective
cir·ca·di·an
(ˌ)sər-ˈkad-ē-ən, -ˈkād-; ˌsər-kə-ˈdī-ən, -ˈdē-
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