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

Limit light at night Light is one of the most significant drivers of your circadian rhythm, according to Joanna Fong-Isariyawongse, MD, sleep neurologist at the University of Pittsburgh Medical Center. —Ashley Abramson, Allure, 13 Feb. 2025

The human body thrives on routine, and waking up at the same time every morning can regulate your circadian rhythm (the body's internal clock). —Lana Barhum, Verywell Health, 12 Feb. 2025

Getting sun exposure, especially early in the day, also aids in brain and mood health and can regulate your circadian rhythm. —Angelica Stabile, Fox News, 12 Feb. 2025

While some babies naturally sleep through the night early on, others can take months—if not longer—to fall into a regular circadian rhythm. —Lauryn Higgins, Parents, 3 Feb. 2025

Word History

Etymology

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

First Known Use

1959, in the meaning defined above

Rhymes for circadian

• acadian
• akkadian
• arcadian
• palladian
• radian

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Medical Definition

circadian

adjective

cir·​ca·​di·​an (ˌ)sər-ˈkad-ē-ən, -ˈkād-; ˌsər-kə-ˈdī-ən, -ˈdē- 

: 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