ephemeron
noun
ephem·er·on
ə̇ˈfeməˌrän
plural ephemera -m(ə)rə 
also ephemerons
also ephemerons -məˌränz
1
: ephemerid
2
: ephemeral entry 2
Word History
Etymology
New Latin, from Greek ephemēron May fly, from neuter of ephemēros lasting a day, short-lived, daily