circadian

adjective

cir·​ca·​di·​an sər-ˈkā-dē-ən How to pronounce circadian (audio)
: 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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Half of all meetings occur between 9:00 a.m. and 11:00 a.m. and 1:00 p.m. and 3:00 p.m., precisely when neuroscientists identify natural productivity peaks due to circadian rhythms. Caroline Castrillon, Forbes.com, 18 June 2025 Wellness takes priority on every Four Seasons jet trip: All itineraries fly west to minimize jet lag (westward travel aligns better with the body’s circadian rhythm), and there are no overnight flights, to ensure guests enjoy a dreamy night’s sleep in their Four Seasons beds. Alexandra Kirkman, Fortune, 18 June 2025 Light’s ability to influence our mood and well-being is supported by scientific studies that demonstrate its profound impact on the body’s circadian rhythm, hormone regulation, and brain function. Sophie Flaxman, Better Homes & Gardens, 15 June 2025 The in-room AM + PM Rituals Program, for example, leads guests through meditation and movement on a massive TV to improve circadian rhythms. Alisha Prakash, Travel + Leisure, 14 June 2025 See All Example Sentences for circadian

Word History

Etymology

Latin circa about + dies day + English -an entry 2 — more at deity

First Known Use

1959, in the meaning defined above

Time Traveler
The first known use of circadian was in 1959

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Cite this Entry

“Circadian.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/circadian. Accessed 2 Jul. 2025.

Medical Definition

circadian

adjective
: being, having, characterized by, or occurring in approximately 24-hour periods or cycles (as of biological activity or function)
circadian periodicity
circadian rhythms in behavior or physiological activity
compare infradian, ultradian
Last Updated: - Updated example sentences
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