Mongolian People's Republic vs Outer Mongolia

Mongolian People's Republic and Outer Mongolia both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mongolian People's Republic	Yes	No	No	No
Outer Mongolia	Yes	No	No	No

As nouns, Mongolian People's Republic and Outer Mongolia are synonyms defined as:

Mongolian People's Republic and Outer Mongolia: a landlocked socialist republic in central Asia

Other synonyms of Mongolian People's Republic include Mongolia.

Mongolian People's Republic (noun)	Outer Mongolia (noun)
a landlocked socialist republic in central Asia	a landlocked socialist republic in central Asia