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Like many other fields, science has its own style of communication full of specific jargon and guided by unwritten rules.  Most of the posts on this blog focus on breaching this barrier to the public’s understanding and appreciation of science.  In this series, I’d like to take another approach by highlighting scientific words which have escaped the confines of jargon to reach a broader appeal because of their sound or their evocative power as metaphors.  Today’s uncommon but useful word is nychthemeron. [Previous words: petrichor, alluvium]

Nychthemeron (pronounced nik-themaron and sometimes spelled nycthemeron) simply means a 24 hour period — that is, a day and a night.  In fact, it literally translates as night-day, being an amalgam of the Greek words nyct (night) and hemera (day).  Nychthemeron has primarily been used in various kinds of technical writing to overcome the ambiguity inherent in the word “day”.  Interestingly, it seems that “day” doesn’t come from the Latin dies, but rather from the Sanskrit verb dah, meaning “to burn”.  Although the Online Etymology Dictionary claims that day originally meant “daylight hours”, one of the earliest quotation in the Oxford English Dictionary is from Ælfric’s Anglo-Saxon Bible, where it’s used to mean a nychthemeron.  The earliest use of nychthemeron cited in the OED is from 1682 in Henry More’s annotations of Lux Orientalis: “Onely the shadowy Vale of the Night will be cast over them once in a Nycthemeron.”  Five years earlier, Robert Cary used an alternative spelling in his Palæologica Chronica: “They came to hit upon the number of 360 Days in the first place, concluding..that in so many Nuchthemerinal Revolutions, the Sun came to the same τροπή,..where he was the Year before.”  It’s continued to be used in technical contexts since then; just last year, Clément Bougard and his colleagues wrote: “Although several studies have reported that postural control is influenced by the time-of-day, only a few were conducted across an entire nychthemeron.”

I think it’s a shame that nychthemeron is mainly confined to technical treatises.  It really is a wonderful word, perfectly filling a gap that I never quite realized existed.  Discovering it was like eating an exquisite hors d’oeuvre: it seems insignificant at first, but turns out to be full of splendour and richness.  Now that I know it exists, I’m eager to use it in a story or a poem!

“The dawn and gloaming most invite one to Musement; but I have found no watch of the nychthemeron that has not its own advantages for the pursuit.”

Charles Pierce
The Hibbert Journal: a quarterly review of religion, theology, and philosophy; vol 7 93, 1908
(via Oxford English Dictionary)

Finnish has an equivalent word, vuorokausi (vuoro=”turn”; kausi=”period”), though unlike nychthemeron, it isn’t considered a technical term and is very commonly used.  Do you know any other languages with a word for a nychthemeron?