an ancient device for measuring time by the regulated flow of water or mercury through a small aperture.
Origin: 1640–50; < L < Gk klepsýdra, equiv. to kleps- (klep-, s. of kléptein to steal, conceal + -s- formative in derivation) + hydra, deriv. of hýdōr water
clep·sy·dra (klěp'sĭ-drə) n.
pl.clep·sy·dras or clep·sy·drae (-drē') An ancient device that measured time by marking the regulated flow of water through a small opening. Also called water glass.
[Latin, from Greek klepsudra : kleptein, kleps-, to steal + hudōr, water; see wed-1 in Indo-European roots.]