police wagon vs wagon

police wagon and wagon both are nouns.

Word	Noun	Adjective	Verb	Adverb
police wagon	Yes	No	No	No
wagon	Yes	No	No	No

As nouns, police wagon and wagon are synonyms defined as:

Other synonyms of police wagon include black Maria, paddy wagon, patrol wagon, police van.

police wagon (noun)	wagon (noun)
van used by police to transport prisoners	any of various kinds of wheeled vehicles drawn by an animal or a tractor
	a car that has a long body and rear door with space behind rear seat
	van used by police to transport prisoners
	a child's four-wheeled toy cart sometimes used for coasting