A water clock, or clepsydra (from Ancient Greek κλεψύδρα (klepsúdra) ‘pipette, water clock’; from κλέπτω (kléptō) ‘to steal’ and ὕδωρ (hydor) ‘water’; lit. ’ water thief’), is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount of liquid can then be measured.