Circadian (adjective, “Sir-KAY-dee-in”)
A period of about 24 hours. Rhythms that vary over a 24-hour period are described as circadian. Our sleep schedules are circadian. Similar 24-hour rhythms are found in other animals as well as plants, fungi and even bacteria.
In a sentence
When we stay up late reading on a brightly lit device, the light and late hours may mess with our circadian rhythm and disrupt our sleep.
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circadian Recurring naturally on a 24-hour cycle.
circadian rhythm Biological functions such as body temperature and sleeping/waking times that operate on a roughly 24-hour cycle.