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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Unsurprisingly, it has been shown to disrupt our circadian rhythms (the 24-ish hour cycles that regulate how our bodies function, including our wake-sleep cycle).
—
Laurie Winkless, Forbes.com, 23 July 2025
Light, especially sunlight, regulates the sleep and wake cycle, known as your circadian rhythm.
—Ashley Olivine, Verywell Health, 23 July 2025
The researchers showed how the interplay between a baby's rising sleep pressure and immature circadian rhythms can create seemingly erratic nap behavior that, in reality, follows a mathematically predictable pattern.
—Daniella Gray, MSNBC Newsweek, 23 July 2025
The body’s internal clock, called the circadian rhythm, plays an important role in how efficiently your body changes food into energy and how weight can be managed.
—Bethany Thayer, Freep.com, 19 July 2025
See All Example Sentences for circadian
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Laurie Winkless, Forbes.com, 23 July 2025
Light, especially sunlight, regulates the sleep and wake cycle, known as your circadian rhythm.
—Ashley Olivine, Verywell Health, 23 July 2025
The researchers showed how the interplay between a baby's rising sleep pressure and immature circadian rhythms can create seemingly erratic nap behavior that, in reality, follows a mathematically predictable pattern.
—Daniella Gray, MSNBC Newsweek, 23 July 2025
The body’s internal clock, called the circadian rhythm, plays an important role in how efficiently your body changes food into energy and how weight can be managed.
—Bethany Thayer, Freep.com, 19 July 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 7 Aug. 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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