police academy vs academy

police academy and academy both are nouns.

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

As nouns, academy is a hypernym of police academy; that is, academy is a word with a broader meaning than police academy:

police academy (noun)	academy (noun)
an academy for training police officers	a learned establishment for the advancement of knowledge
	a secondary school (usually private)
	a school for special training
	an institution for the advancement of art or science or literature