Word of the Day

: June 27, 2010

circadian

adjective ser-KAY-dee-un

What It Means

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

circadian in Context

"Teenagers, like everyone else, need bright lights in the morning … to synchronize their inner, circadian rhythms with nature's cycles of day and night." (Thomas H. Maugh II, Chicago Tribune, Feb. 17, 2010)

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."