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.
      [1913 Webster]

   2. Short-lived; existing or continuing for a short time only.
      "Ephemeral popularity." --V. Knox.
      [1913 Webster]

            Sentences not of ephemeral, but of eternal,
            efficacy.                             --Sir J.
                                                  Stephen.
      [1913 Webster]

   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.
      [1913 Webster]