Webster’s Revised Unabridged Dictionary · 1913
Dayfly
Day′fly′ (dā′flī′), n. (Zoöl.) A neuropterous insect of the genus Ephemera and related genera, of many species, and inhabiting fresh water in the larval state; the ephemeral fly; — so called because it commonly lives but one day in the winged or adult state. See Ephemeral fly, under Ephemeral.