ephemeral: [16] Ephemeral, now used fairly loosely for ‘transitory’, originally meant specifically ‘lasting only one day’. It comes from Greek ephémeros, a compound formed from the prefix epí- ‘on’ and hēmérā ‘day’. The Greeks named the mayfly ephémeron, since its adult form lives only one day, and English adopted ephemeron [16] as the scientific name for the insect.
1560s; see ephemera + -al (1). Originally of diseases and lifespans, "lasting but one day;" extended sense of "transitory" is from 1630s. Related: Ephemerally; ephemerality.
