city vs Rio

city and Rio both are nouns.

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

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