noun
(also nychthemeron)
A period of twenty-four hours, consisting of a day and a night.
Origin
Late 17th century; earliest use found in Henry More (1614–1687), philosopher, poet, and theologian. From Hellenistic Greek νυχθήμερον period of a day and a night, use as noun of neuter singular of νυχθήμερος lasting for a day and a night from ancient Greek νυκτ-, νύξ night + ἡμέρα day.
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