ephemeral(n = noun.animal) ephemeron - anything short-lived, as an insect that lives only for a day in its winged form;
is a kind of insect

   ephemeral(s = adj.all) fugacious, passing, short-lived, transient, transitory - lasting a very short time; "the ephemeral joys of childhood"; "a passing fancy"; "youth's transient beauty"; "love is transitory but it is eternal"; "fugacious blossoms"
Derived forms noun ephemera₁, noun ephemerality₁, noun ephemeralness₁

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. V. Knox. [1913 Webster]
"Sentences not of ephemeral, but of eternal, efficacy." [1913 Webster]

   Anything lasting but a day, or a brief time; an ephemeral plant, insect, etc. [1913 Webster]

ephemeral, adj.
1 lasting or of use for only a short time; transitory.
2 lasting only a day.
3 (of an insect, flower, etc.) lasting a day or a few days.

Derivative:
ephemerality n. ephemerally adv. ephemeralness n.

Etymology:
Gk ephemeros: see EPHEMERA

N  transience, transientness, evanescence, impermanence, fugacity, caducity, mortality, span, nine days' wonder, bubble, Mayfly, spurt, flash in the pan, temporary arrangement, interregnum, velocity, suddenness, changeableness, transient, transient boarder, transient guest, transient, transitory, transitive, passing, evanescent, fleeting, cursory, short-lived, ephemeral, flying, fugacious, fugitive, shifting, slippery, spasmodic, instantaneous, momentaneous, temporal, temporary, provisional, provisory, deciduous, perishable, mortal, precarious, unstable, insecure, impermanent, brief, quick, brisk, extemporaneous, summary, pressed for time, sudden, momentary, temporarily, pro tempore, for the moment, for a time, awhile, en passant, in transitu, in a short time, soon, briefly, at short notice, on the point of, on the eve of, in articulo, between cup and lip, one's days are numbered, the time is up, here today and gone tomorrow, non semper erit aestas, eheu! fugaces labuntur anni, sic transit gloria mundi, a schoolboy's tale, the wonder of the hour!, dum loquimur fugerit invidia aetas, fugit hora, all that is transitory is but an illusion.