res publica vs political entity

res publica and political entity both are nouns.

Word	Noun	Adjective	Verb	Adverb
res publica	Yes	No	No	No
political entity	Yes	No	No	No

As nouns, political entity is a hypernym of res publica; that is, political entity is a word with a broader meaning than res publica:

res publica: a politically organized body of people under a single government
political entity: a unit with political responsibilities

Other hypernyms of res publica include political unit.

res publica (noun)	political entity (noun)
a politically organized body of people under a single government	a unit with political responsibilities