Definitions for water clock
Random House Webster's College Dictionary
a device, as a clepsydra, for measuring time by the flow of water.
Origin of water clock:
water clock, clepsydra, water glass(noun)
clock that measures time by the escape of water
A device for measuring time by letting water flow out of a container, usually through a tiny aperture.
an instrument or machine serving to measure time by the fall, or flow, of a certain quantity of water; a clepsydra