Ephemeral, 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. Stephen. Ephemeral fly (Zoöl.), 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 larvæ are aquatic; -- called also day fly and May fly.
1 other Webster entry under this spelling
Ephemeral, n.
Anything lasting but a day, or a brief time; an ephemeral plant, insect, etc.
Shades of meaning
Fernald has no entry of its own for ephemeral; he lists it under transient.
Where he writes about it:
Ephemeral (Gr. epi, on, and hemera, day) literally lasting but for a day, often marks more strongly than transient exceeding brevity of duration; it agrees with transitory in denoting that its object is destined to pass away, but is stronger, as denoting not only its certain but its speedy extinction; thus that which is ephemeral is looked upon as at once slight and perishable, and the word carries often a suggestion of contempt; man's life is transitory, a butterfly's existence is ephemeral; with no solid qualities or worthy achievements a pretender may sometimes gain an ephemeral popularity. — from transient