1. An ancient device that measured time by marking the regulated flow of water through a small opening; also called a water glass: The clepsydras were used in Egypt during c.2000 BC; then from Egypt, they were introduced into Greece and later from there into Rome.
2. Etymology: from Latin which came from Greek klepsudra; from kleps-, "to steal" + hudor, "water"; with the allusion that the water is flowing stealthily (flowing secretly) from it.