posse vs police force

posse and police force both are nouns.

Word	Noun	Adjective	Verb	Adverb
posse	Yes	No	No	No
police force	Yes	No	No	No

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

Other hypernyms of posse include constabulary, law, police.

posse (noun)	police force (noun)
a temporary police force	the force of policemen and officers