Word of the Day:

: being, having, characterized by, or occurring in approximately 24-hour periods or cycles (as of biological activity or function)

The presence and absence of light can greatly influence an organism's circadian rhythms.

"The circadian cycle is a period of approximately 24 hours. During that time, and keyed to the daily shift from light to dark and back again, the circadian clock influences rhythmic changes in both physiology and behavior." — Eve Glazier and Elizabeth Ko, The Bismarck Tribune, 3 July 2018

More example sentences

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.