water glass vs clepsydra

water glass and clepsydra both are nouns.

Word	Noun	Adjective	Verb	Adverb
water glass	Yes	No	No	No
clepsydra	Yes	No	No	No

As nouns, water glass and clepsydra are synonyms defined as:

water glass and clepsydra: clock that measures time by the escape of water

Other synonyms of water glass include water clock.

water glass (noun)	clepsydra (noun)
a glass for drinking water	clock that measures time by the escape of water
gauge for indicating the level of water in e.g. a tank or boiler or reservoir
clock that measures time by the escape of water
a viscous glass consisting of sodium silicate in solution; used as a cement or as a protective coating and to preserve eggs