Looking for a word like "ephemeral," which is derived from Latin "ephēmeros," meaning "lasting only a day," according to the Oxford Dictionary of English.

However, I'd like a word that means "lasting only a night." Does such a word exist?

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    Ephēmeros isn't Latin, it's Greek (ἐφήμερος, from ἐπί 'on' + ἡμέρα 'day' + -(ι)ος); it was borrowed into Neo-Latin as ephemerus, seemingly with a short e. There's a structurally parallel word ἐπινύκτιος (which could be latinised as epinyktius, I guess), but in practice it just means 'by night, nightly'.
    – Cairnarvon
    Commented Jan 11, 2023 at 2:15
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    While the etymology may refer to one day, the word now means "lasting for a very short time". There's no specific time period implied. The example sentence in my dictionary is "Fashions are ephemeral", meaning a few months.
    – Barmar
    Commented Jan 11, 2023 at 17:16
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    @Barmar Metaphorical usage was already common in antiquity.
    – cmw
    Commented Jan 11, 2023 at 20:53

2 Answers 2


While Greek ἐφήμερος (ephēmeros) literally means "for one day", it was often used metaphorically to refer to anything that lasts a short time. For example, mortals were ephēmeroi in the eyes of the gods: our lifespans might as well be a single day, compared to an immortal.

As such, I'd use this word for something like the ogre-faced spider's eyes, which last for one night and then burn away at sunrise. The counterpart ἐπινύκτιος (epinyktios) was, as far as I can tell, never used for this meaning: it specifically meant "by night", not "lasting only a single night".

Similarly, Latin pernox generally emphasizes how long something lasts, not how short it lasts: more like "the party was still going all night" or "I was studying all through the night" in its connotations. (It often refers specifically to the full moon, since when the moon is full it rises at sunset and sets at sunrise: it's around all through the night.)

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    Thanks fort those precisions. Still you can admit, this is the closest we could find to what the op wanted, beautiful word. @Manuel You found it so quickly lol... Commented Jan 11, 2023 at 18:20
  • I was looking for "nightly" last week, And I saw a lot of word about night.😆
    – user11898
    Commented Jan 11, 2023 at 19:45
  • Seems ἐφήμερος also had that meaning, as indicated by section II in the LSJ. Clearest example is "γυμνασία Ascl. Tact. 1.4."
    – cmw
    Commented Jan 11, 2023 at 20:55
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    Thank you for that delightful information about the spider's eyes :) Commented Jan 12, 2023 at 1:45
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    To clarify about the eyes of the ogre-faced spider, which is something I hadn’t known about before and did some digging on—thank your for that reference it’s great—the entire eye doesn’t burn away, but a highly-photosensitive layer, I guess analogous to our retinas, does burn away each morning and have to be regrown each night.
    – KRyan
    Commented Jan 12, 2023 at 15:01

There's the adjective pernox it means "continuing through the night, that lasts all night"

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    This is amazing that a word exists with the exact fine-grained denotation that lemonlemon was looking for. What a cool language! Commented Jan 11, 2023 at 7:56
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    @VincentKrebs I think the denotation is actually the opposite of ephemerus, as Draconis says in his answer: pernox doesn't mean "lasting only one night", but "lasting all night".
    – TKR
    Commented Jan 11, 2023 at 18:20
  • @TKR Yes I know, as it can be easily deduced from the meaning of per. But still ;) Commented Jan 11, 2023 at 18:21

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