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

Circadian Phase Alignment maps stimuli such as stress and exercise against circadian rhythm to recommend ideal times to go to bed and wake up. —PCMAG, 24 Jan. 2025

Smart alarm clocks wake you during your lightest sleep phase, while circadian rhythm apps help optimize light exposure, caffeine, and sleep timing for a smoother adjustment. —Maria Sokolina, Forbes, 22 Jan. 2025

The new study highlights that drinking coffee in the afternoon can disrupt circadian rhythms, which reduces melatonin production. —Stephanie Brown, Verywell Health, 18 Jan. 2025

For those working the night shift, Smith said employees may find relief by using light exposure to readjust their circadian rhythms. —Julianna Bragg, CNN, 15 Jan. 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

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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