prisoner of war vs prisoner

prisoner of war and prisoner both are nouns.

Word	Noun	Adjective	Verb	Adverb
prisoner of war	Yes	No	No	No
prisoner	Yes	No	No	No

As nouns, prisoner is a hypernym of prisoner of war; that is, prisoner is a word with a broader meaning than prisoner of war:

prisoner of war: a person who surrenders to (or is taken by) the enemy in time of war
prisoner: a person who is confined; especially a prisoner of war

Other hypernyms of prisoner of war include captive.

prisoner of war (noun)	prisoner (noun)
a person who surrenders to (or is taken by) the enemy in time of war	a person who is confined; especially a prisoner of war