Nychthemeron /nɪkˈθɛmərɒn/, occasionally nycthemeron or nuchthemeron, is a period of 24 consecutive hours. It is sometimes used, especially in technical literature, to avoid the ambiguity inherent in the term day.

The Nychthemeron Clock in Snowshill Manor, Gloucestershire, UK

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.


It is a loanword from Ancient Greek νυχθήμερον (nukhthḗmeron), which appears in the New Testament.[1] This is a noun use of the neuter singular form of Ancient Greek: νυχθήμερος, romanizednukhthḗmeros, lit.'lasting a day and night', from νύξ (núx, “night”) + ἡμέρα (hēméra, “day”).

In other languagesEdit

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 Family 24 hours Sunlit state
Danish Germanic døgn dag
Norwegian (Bokmål) Germanic døgn dag
Norwegian (Nynorsk) Germanic døgn, døger dag
Swedish Germanic dygn dag
Icelandic Germanic sólarhringur ("sun-circle") dagur
Faroese Germanic samdøgur dagur
Old Norse Germanic dǿgr, dǿgn dagr
North Frisian Germanic eetlem däi
West Frisian Germanic etmel dei
Dutch Germanic etmaal dag
Esperanto International auxiliary language diurno,[2] tagnokto[3] ("day-night") tago
Finnish Uralic vuorokausi ("turn-period") päivä
Estonian Uralic ööpäev ("night-day") päev
North Sámi Uralic jándor beaivi
Latvian Baltic diennakts ("day-night") diena
Lithuanian Baltic para diena
Polish Slavic doba dzień
Russian Slavic сутки [ˈsutkʲɪ] день
Hebrew Semitic יממה יום
Bulgarian Slavic денонощие ("day-night") ден
Bengali Indo-Aryan দিবারাত্রি, দিনরাত দিন
Sanskrit Indo-Aryan अहोरात्र दिन
Tamil Tamil நாள் பகல்
Ukrainian Slavic доба день
Swahili Bantu siku mchana
Indonesian/Malay Malayic hari siang
Japanese Japonic
Korean Koreanic
Kannada Kannada–Badaga ದಿನ ಹಗಲು
German Germanic Etmal Lichter Tag
Welsh Celtic diwrnod; dwthwn ('that day') dydd
Yiddish Germanic ֵמֵעֵת לְעֵת טאָג

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


  1. ^ Liddell, Henry George; Scott, Robert (1889), An Intermediate Greek-English Lexicon, Oxford: Clarendon Press.
  2. ^ diurn/o in Reta Vortaro
  3. ^ nokt/o in Reta Vortaro