circadian

adjective

cir·ca·di·an | \ sər-ˈkā-dē-ən

Definition of circadian

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

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Did You Know?

Just over fifty years ago, no one talked about "circadian rhythms" - because "circadian" hadn't even been coined yet. In 1959, a scientist formed the word from the Latin words circa ("about") and "dies" ("day"), and it caught on quickly. "Circadian" appeared in periodicals throughout the sixties, and appeared in a Merriam-Webster dictionary before the decade was up. 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

In advanced sleep phase, your body clock (circadian rhythm) is on a schedule hours earlier than most other people’s. — baltimoresun.com, "Are you an ‘extreme early bird’?," 11 Sep. 2019 In advanced sleep phase, your body clock (circadian rhythm) is on a schedule hours earlier than most other people’s. — baltimoresun.com, "Are you an ‘extreme early bird’?," 11 Sep. 2019 In advanced sleep phase, your body clock (circadian rhythm) is on a schedule hours earlier than most other people’s. — baltimoresun.com, "Are you an ‘extreme early bird’?," 11 Sep. 2019 In advanced sleep phase, your body clock (circadian rhythm) is on a schedule hours earlier than most other people’s. — chicagotribune.com, "Are you an ‘extreme early bird’?," 20 Aug. 2019 Plants, like people, have circadian rhythms that alter their responses to their environment. — Zoë Schlanger, Quartz, "Syngenta just funded a study on the best way to spray glyphosate," 16 Aug. 2019 The circadian rhythm regulates the sleep-wake cycle. — Lauren Lee, CNN, "These interior design tips can help you create a bedroom blueprint for better sleep," 6 Aug. 2019 Light disrupts the normal cues associated with circadian rhythms, to which species have evolved timing of migration, reproducing, and feeding. — Jenny Howard, National Geographic, "Marine pollution, explained," 2 Aug. 2019 Another group—also at the Institute of Neuroscience—recently combined cloning and CRISPR to create 325 monkey embryos with the same mutation, one that disrupts circadian rhythms in people and is connected to sleep disorders, diabetes, and cancers. — Jon Cohen, Science | AAAS, "China’s CRISPR push in animals promises better meat, novel therapies, and pig organs for people," 31 July 2019

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'circadian.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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Last Updated

15 Oct 2019

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The first known use of circadian was in 1959

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More Definitions for circadian

circadian

adjective

English Language Learners Definition of circadian

technical : relating to the regular changes in a person or thing that happen in 24-hour periods

See the full definition for circadian in the English Language Learners Dictionary

circadian

adjective

cir·ca·di·an | \ (ˌ)sər-ˈkad-ē-ən, -ˈkād-; ˌsər-kə-ˈdī-ən, -ˈdē-

Medical Definition of circadian

: 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