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.
Cite this Entry
“Circadian.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/circadian. Accessed 4 Sep. 2026.
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