The Collaborative International Dictionary of English v.0.48:
Ephemeral \E*phem"er*al\, a.
1. Beginning and ending in a day; existing only, or no longer
than, a day; diurnal; as, an ephemeral flower.
2. Short-lived; existing or continuing for a short time only.
"Ephemeral popularity." --V. Knox.
Sentences not of ephemeral, but of eternal,
efficacy. --Sir J.
Ephemeral fly (Zo["o]l.), one of a group of neuropterous
insects, belonging to the genus Ephemera and many allied
genera, which live in the adult or winged state only for a
short time. The larv[ae] are aquatic; -- called also day
fly and May fly.