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.
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Additional causes of sleepiness Sleep disorders such as sleep apnea, insomnia, restless leg syndrome and circadian rhythm sleep disorders, as well as chronic pain conditions and medications can also contribute to sleepiness, which will be ruled out by a sleep specialist.
—
Sandee Lamotte, CNN Money, 14 Apr. 2025
Our circadian rhythms, 24-hour cycles governed by the brain’s suprachiasmatic nucleus, regulate everything from body temperature to hormone release.
—Ximena Araya-Fischel, Forbes.com, 12 Apr. 2025
Frequent travel across multiple time zones disrupts circadian rhythms and increases the risk of injuries due to inadequate rest and recovery.
—Claire Poole, Forbes.com, 5 Apr. 2025
The time change also brings with it other adverse health impacts due to changes in our circadian rhythm.
—Simmone Shah, TIME, 5 Mar. 2025
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Sandee Lamotte, CNN Money, 14 Apr. 2025
Our circadian rhythms, 24-hour cycles governed by the brain’s suprachiasmatic nucleus, regulate everything from body temperature to hormone release.
—Ximena Araya-Fischel, Forbes.com, 12 Apr. 2025
Frequent travel across multiple time zones disrupts circadian rhythms and increases the risk of injuries due to inadequate rest and recovery.
—Claire Poole, Forbes.com, 5 Apr. 2025
The time change also brings with it other adverse health impacts due to changes in our circadian rhythm.
—Simmone Shah, TIME, 5 Mar. 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 Apr. 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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