peace vs Pax Romana

peace and Pax Romana both are nouns.

Word	Noun	Adjective	Verb	Adverb
peace	Yes	No	No	No
Pax Romana	Yes	No	No	No

As nouns, Pax Romana is a hyponym of peace; that is, Pax Romana is a word with a more specific, narrower meaning than peace:

peace: the state prevailing during the absence of war
Pax Romana: the Roman peace; the long period of peace enforced on states in the Roman Empire

Other hyponyms of peace include amity, armistice, cease-fire, truce, conciliation, collective security.

peace (noun)	Pax Romana (noun)
a treaty to cease hostilities	the Roman peace; the long period of peace enforced on states in the Roman Empire
the absence of mental stress or anxiety
the state prevailing during the absence of war
harmonious relations; freedom from disputes
the general security of public places