body politic vs res publica

body politic and res publica both are nouns.

Word	Noun	Adjective	Verb	Adverb
body politic	Yes	No	No	No
res publica	Yes	No	No	No

As nouns, body politic and res publica are synonyms defined as:

body politic and res publica: a politically organized body of people under a single government

Other synonyms of body politic include commonwealth, country, land, nation, state.

body politic (noun)	res publica (noun)
a politically organized body of people under a single government	a politically organized body of people under a single government