Nychthemeron
//nɪkˈθi.mə.ɹɑn// noun
noun ·Rare ·Advanced level
Definitions
Noun
- 1 A period of one day and one night, a date: in the West, a period of 24 consecutive hours. uncommon
"It has not yet been found by Observation, whether Mercury turns upon its own Axis, ... that is, whether it has the vicissitude of Day and Night, much less what is the space of its Nychthemeron or Natural Day; but one may safely enough conjecture that it does revolve about its Axis, since the other Planets do."
Example
More examples"A nychthemeron has eighty-six thousand four hundred seconds."
Etymology
From Ancient Greek νυχθήμερον (nukhthḗmeron), noun use of the neuter singular form of νυχθήμερος (nukhthḗmeros, “lasting a day and night”), from νύξ (núx, “night”) + ἡμέρα (hēméra, “day”).
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Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.