floodgate vs water gate

floodgate and water gate both are nouns.

Word	Noun	Adjective	Verb	Adverb
floodgate	Yes	No	No	No
water gate	Yes	No	No	No

As nouns, floodgate and water gate are synonyms defined as:

floodgate and water gate: regulator consisting of a valve or gate that controls the rate of water flow through a sluice

Other synonyms of floodgate include head gate, penstock, sluice valve, sluicegate.

floodgate (noun)	water gate (noun)
regulator consisting of a valve or gate that controls the rate of water flow through a sluice	regulator consisting of a valve or gate that controls the rate of water flow through a sluice
something that restrains a flood or outpouring