Rio de Janeiro vs city

Rio de Janeiro and city both are nouns.

Word	Noun	Adjective	Verb	Adverb
Rio de Janeiro	Yes	No	No	No
city	Yes	No	No	No

Rio de Janeiro (noun)	city (noun)
the former capital and 2nd largest city of Brazil; chief Brazilian port; famous as a tourist attraction	people living in a large densely populated municipality
	a large and densely populated urban area; may include several independent administrative districts
	an incorporated administrative district established by state charter