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The Nychthemeron Clock in Snowshill Manor, Gloucestershire, UK

Nychthemeron /nɪkˈθɛmərɒn/, occasionally nycthemeron or nuchthemeron (Greek νυχθήμερον from the words nykt- "night", and hemera "day, daytime"), is a period of 24 consecutive hours. It is sometimes used, especially in technical literature, to avoid the ambiguity inherent in the term day.

It is the period of time that a calendar normally labels with a date, although a nychthemeron simply designates a time-span that can start at any time, not just midnight.

In other languages[edit]

Some languages have a word for 24 hours, or more loosely a day plus a night in no particular order. Unlike a calendar date, only the length is defined, with no particular start or end. Furthermore, these words are considered basic and native to these languages, so unlike "nychthemeron", they are not associated with jargon.

Words for 24 hours are listed in the middle column. For comparison, the word for day, in the meaning of daytime, the sunlit state, the opposite of night, is also listed in the rightmost column:

Language 24 hours sunlit state
Danish døgn dag
Norwegian (Bokmål) døgn dag
Norwegian (Nynorsk) døger dag
Swedish dygn dag
Icelandic sólarhringur ("sun-circle") dagur
Faroese samdøgur dagur
North Frisian eetlem däi
West Frisian etmel dei
Dutch etmaal dag
Esperanto diurno,[1] tagnokto[2] ("day-night") tago
Finnish vuorokausi ("turn-period") päivä
Estonian ööpäev ("night-day") päev
Latvian diennakts ("day-night") diena
Lithuanian para diena
Russian сутки [ˈsutkʲɪ] день
Hebrew יממה יום
Bulgarian денонощие ("day-night") ден
Bengali দিবারাত্রি, দিনরাত দিন
Sanskrit अहोरात्र दिन
Tamil நாள் பகல்
Polish doba dzień
Ukrainian доба день

The word dag, as in the Nordic languages, is etymologically the same as day in English.


  1. ^ diurn/o in Reta Vortaro
  2. ^ nokt/o in Reta Vortaro