Meaning of nycthemeron in English:

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.