water clock vs clock

water clock and clock both are nouns.

Word	Noun	Adjective	Verb	Adverb
water clock	Yes	No	No	No
clock	Yes	No	Yes	No

As nouns, clock is a hypernym of water clock; that is, clock is a word with a broader meaning than water clock:

water clock (noun)	clock (noun)
clock that measures time by the escape of water	a timepiece that shows the time of day

water clock (verb)	clock (verb)
	measure the time or duration of an event or action or the person who performs an action in a certain period of time