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

Lighting As Energy And Mood Management Alongside a growing recognition of circadian rhythms’ importance, forward-thinking companies are investing in better lighting technologies as part of broader efforts to cultivate more attractive, health-promoting work environments. —Julian Hayes Ii, Forbes.com, 30 Apr. 2025

Hormone Levels Hormones and other body chemicals are linked to your circadian rhythm. —Rachael Zimlich, Bsn, Rn, Verywell Health, 25 Apr. 2025

Tips for How To Sleep on a Plane During travel, these techniques can help improve the comfort of your surrounding environment and regulate your circadian rhythm (your body's internal clock).1 1. —Laura Schober, Health, 23 Apr. 2025

Activities in our cells occur cyclically, according to our circadian rest-wake cycles. —Sharon Horesh Bergquist, Flow Space, 24 Mar. 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