Nychthemeron


Nychthemeron, 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, which appears in the New Testament. This is a noun use of the neuter singular form of nukhthḗmeros, from νύξ + ἡμέρα.

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 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:
Language24 hoursSunlit state
Danishdøgndag
Norwegian døgndag
Norwegian døgn, døgerdag
Swedishdygndag
Icelandicsólarhringur dagur
Faroesesamdøgurdagur
Old Norsedǿgr, dǿgndagr
North Frisianeetlemdäi
West Frisianetmeldei
Dutchetmaaldag
Esperantodiurno, tagnokto tago
Finnishvuorokausi päivä
Estonianööpäev päev
Latviandiennakts diena
Lithuanianparadiena
Polishdobadzień
Russianсутки день
Hebrewיממהיום
Bulgarianденонощие ден
Bengaliদিবারাত্রি, দিনরাতদিন
Sanskritअहोरात्रदिन
Tamilநாள்பகல்
Ukrainianдобадень
Swahilisikumchana
Indonesian/Malayharisiang
Japanese日昼
Korean일낮
Kannadaದಿನಹಗಲು

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