circadian

American  

[sur-key-dee-uhn] / sɜrˈkeɪ di ən /

adjective

Physiology.

1. of or relating to a biorhythm or regular biological cycle occurring once every 24 hours, such as waking and sleeping.

   Exposure to blue light at night can disrupt your circadian rhythm, making your biological clock think it's earlier in the day rather than time for bed.

   He is doing research related to the circadian cycling of hormones.

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circadian British  

/ sɜːˈkeɪdɪən /

adjective

1. of or relating to biological processes that occur regularly at about 24-hour intervals, even in the absence of periodicity in the environment See also biological clock

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Etymology

Origin of circadian

First recorded in 1955–60; from circā “about” + Latin di(ēs) “day” + -an ( def. ); see circa ( def. )

Explanation

Something that's circadian happens on a regular, daily basis. Your body's circadian rhythm is made up of processes that occur regularly every 24 hours. You'll find the word circadian in biology class, or your anatomy and physiology textbook, because it describes a biological process in the human body, as well as in other organisms. Your cycle of sleep, for example, happens on a circadian schedule — approximately every 24 hours, you become tired enough to lie down and close your eyes, a built-in rhythm that's affected somewhat by light. Circadian comes from Latin roots, circa, "about," and diem, "day."

Example Sentences

See Examples For:

circadian

In a world where influencers warn of spiked cortisol levels and disrupted circadian rhythms, plenty of consumers are turning to prebiotic sodas, sugar-free beverages, and refreshers as substitutes.

From Slate ● Aug. 14, 2026

Shapses said she wants to better understand issues such as circadian rhythm, inflammation, metabolic health, and the biochemical issues that help the body sense and respond to food.

From MarketWatch ● Jul. 27, 2026

Stanford professor Jamie Zeitzer, a physiologist who studies circadian cycles and how humans respond to light, supports ending the twice-a-year time changes.

From Los Angeles Times ● Jul. 14, 2026

Dr Victoria Revell, an associate professor in transitional sleep and circadian physiology at the University of Surrey, says this strategy can "help reset the build up of sleepiness you will be experiencing".

From BBC ● Jul. 6, 2026

Not only was this arrangement bad for the astronaut’s circadian rhythm, but the astronaut who was on duty made enough noise as he went about his work to keep his partner awake.

From "Flying to the Moon: An Astronaut's Story" by Michael Collins

Related Words

• constantly
• day-to-day
• everyday
• often
• periodic
• regular
• regularly
• routine