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
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The reason so many people feel off track when daylight savings time ends is because light has a profound effect on the circadian rhythm, the body’s natural 24-hour clock that dictates when one sleeps and wakes.
—
Helen Carefoot, Flow Space, 30 Oct. 2025
Control the Lights Melatonin is a hormone that helps to regulate your body's internal circadian clock.
—Dina Roth Port, Parents, 28 Oct. 2025
Experts say eating within one to two hours of waking helps keep metabolism and circadian rhythms in sync.
—Fran Kritz, Health, 28 Oct. 2025
The biannual time shift tends to affect peoples’ circadian rhythms — the body’s 24-hour clock — which regulate several physiological processes.
—Hannah Poukish
october 27, Miami Herald, 27 Oct. 2025
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Helen Carefoot, Flow Space, 30 Oct. 2025
Control the Lights Melatonin is a hormone that helps to regulate your body's internal circadian clock.
—Dina Roth Port, Parents, 28 Oct. 2025
Experts say eating within one to two hours of waking helps keep metabolism and circadian rhythms in sync.
—Fran Kritz, Health, 28 Oct. 2025
The biannual time shift tends to affect peoples’ circadian rhythms — the body’s 24-hour clock — which regulate several physiological processes.
—Hannah Poukish
october 27, Miami Herald, 27 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 2 Nov. 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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