water gun vs squirt gun

water gun and squirt gun both are nouns.

Word	Noun	Adjective	Verb	Adverb
water gun	Yes	No	No	No
squirt gun	Yes	No	No	No

As nouns, water gun and squirt gun are synonyms defined as:

water gun and squirt gun: plaything consisting of a toy pistol that squirts water

Other synonyms of water gun include squirter, water pistol.

water gun (noun)	squirt gun (noun)
plaything consisting of a toy pistol that squirts water	plaything consisting of a toy pistol that squirts water