From Greek 'ephḗmeros' (lastingonly a day), from epí (on/for) + hēméra (day). Originally a Hippocratic medical term for one-day fevers, it broadened into one of English's most poetic words for transience. ThePIEroot *h₂eh₃mer- (day) connects it to Armenian 'awr' and to the mayfly order Ephemeroptera.
Definition
Lasting for a very short time; transitory, fleeting.
The Full Story
Greek (via Latin)16th centurywell-attested
From Greek 'ephḗmeros' (ἐφήμερος), meaning 'lasting only a day', formed from 'epí' (ἐπί, 'on, for') + 'hēméra' (ἡμέρα, 'day'). The Greek wordwas originally a medical term used by Hippocrates and Galen for fevers that lasted only one day — 'ephḗmeros puretós' (ephemeral fever). Latin borrowed it as 'ephemerus', and the adjective form 'ephemeral' entered English
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The mayfly (order Ephemeroptera — literally 'ephemeral wing') is the living embodiment of the word. Adult mayflies live for as little as 5 minutes to at most 24 hours, just long enough to mate. They have no functional mouths because they don't live long enough to need to
) and 'ephemeron' (the mayfly, the archetypal creature that lives for a single day). The word's journey from clinical fever diagnosis to poetic meditation on transience is one of English's most elegant semantic expansions. Key roots: ἐπί (epí) (Ancient Greek: "on, upon, for (a duration)"), ἡμέρα (hēméra) (Ancient Greek: "day"), *h₂eh₃mer- (Proto-Indo-European: "day").