Nychthemeron

The Nychthemeron Clock in Snowshill Manor, Gloucestershire, UK

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.

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.

Etymology

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

In other languages

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

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