means A delicate, short-lived flying insect of the order Ephemeroptera, whose adults often live only a day or less, just long enough to mate.

from A plain compound of "May" and "fly," named for the late-spring season when great clouds of these insects emerge over rivers and lakes. The scientific name, Ephemeroptera, leans on Greek ephēmeros — "lasting only a day" — the very word that gives us "ephemeral," both pointing at the same brief, glittering life.