clep·sy·dra 
(klĕpsĭ-drə)
(klĕpsĭ-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 klepsudrā : kleptein, kleps-, to steal + hudōr, water; see wed-1 in the Appendix of Indo-European roots.]