ephemerid

From translingual Ephemeridae, from New Latin ephemerus, from Ancient Greek ἐφήμερος (ephḗmeros), the more common form of ἐφημέριος (ephēmérios, “of, for, or during the day, living or lasting but for a day, short-lived, temporary”), from ἐπί (epí, “on”) + ἡμέρα (hēméra, “day”).

来源：wiktionary