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
Did you know?
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
This gradual recalibration softens the circadian shock without majorly disrupting your day-to-day life.
—
Julian Hayes Ii, Forbes.com, 18 Sep. 2025
Disruptive blue wavelengths can wreak havoc on the body’s internal clock, even suppressing the production of melatonin—a hormone that helps regulate our circadian rhythm.
—Laura Kiniry, Popular Science, 17 Sep. 2025
Your skin—and circadian rhythm—will appreciate it.
—Sophia Panych, Allure, 16 Sep. 2025
People who are early birds make up about 15 percent of the population and tend to have circadian cycles shorter than 24 hours, would experience the least circadian burden under permanent daylight saving time as more evening light would extend their circadian cycles closer to 24 hours.
—Hannah Millington, MSNBC Newsweek, 15 Sep. 2025
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Julian Hayes Ii, Forbes.com, 18 Sep. 2025
Disruptive blue wavelengths can wreak havoc on the body’s internal clock, even suppressing the production of melatonin—a hormone that helps regulate our circadian rhythm.
—Laura Kiniry, Popular Science, 17 Sep. 2025
Your skin—and circadian rhythm—will appreciate it.
—Sophia Panych, Allure, 16 Sep. 2025
People who are early birds make up about 15 percent of the population and tend to have circadian cycles shorter than 24 hours, would experience the least circadian burden under permanent daylight saving time as more evening light would extend their circadian cycles closer to 24 hours.
—Hannah Millington, MSNBC Newsweek, 15 Sep. 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 23 Sep. 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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