Circadian Meaning
/səˈkeɪ.dɪ.ən/Definition, CEFR level B2, pronunciation, examples, and quiz.
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Definition
adjOf, relating to, or showing rhythmic behaviour with a period of approximately 24 hours; especially of a biological process.
Sentence Examples
Circadian cycles can be easily appreciated in plants.
Starch degradation is linked to a circadian clock.
CEFR Practice Quiz
The ____ rhythm helps humans feel alert during daytime hours.
CEFR Practice Quiz (Alternate)
Your ____ rhythm is basically your internal clock that regulates city.
Word Origin & History
Etymology tree Proto-Indo-European *(s)ker-der. Ancient Greek κίρκος (kírkos)bor. Latin circus Latin circum Latin circā Proto-Indo-European *dyew- Proto-Indo-European *-s Proto-Indo-European *dyḗws Proto-Italic *djous Latin diēs Proto-Indo-European *-nós Proto-Italic *-nos Latin -nus Latin -ānus Old French -ainder. Middle English -an English -an English circadian From Latin circā (“around”) + diēs (“day”) + English -an. Compare circannual.
Literary Quotations & Historical Citations
"The circadian clock is involved in the regulation of the diurnal sleep-wake cycle, […]."
— 2000, Arnold Sameroff, et al: Handbook of Developmental Psychopathology, page 310:
"To summarize, the circadian system, particularly the SCN, controls the circadian pattern of melatonin release in mammals."
— 2002, Jill B. Becker, Behavioral Endocrinology, page 483:
"The most obvious circadian rhythm is the daily cycle of sleep and activity."
— 2005, Paul Martin, Counting Sheep: The Science and Pleasures of Sleep and Dreams, page 114:
"Circadian clocks developed early in evolution in single-celled organisms, before the animal and plant kingdom split from one another. The original clocks probably functioned to protect the cells from damage induced by high UV radiation."
— 2014 April 5, “Quite interesting: A quietly intriguing column from the brains behind QI, the BBC quiz show. This week; QI orchids you not”, in The Daily Telegraph (Weekend), page W22:
"In addition, the truck driver’s schedule involved sleeping at irregular times, including times when the body’s circadian rhythms are geared toward being awake. He was also awake at times when his circadian rhythms were geared toward being asleep. The time of the crash, about 1:36 a.m., is when sleepiness tends to be greater and performance capabilities are lower."
— 2024, NTSB, Highway Investigation Report, HIR-24-05:
Explore More B2 Vocabulary Words
CEFR Practice Quiz
The ____ rhythm helps humans feel alert during daytime hours.
CEFR Practice Quiz (Alternate)
Your ____ rhythm is basically your internal clock that regulates city.