Rio vs Rio de Janeiro

Rio and Rio de Janeiro both are nouns.

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

As nouns, Rio and Rio de Janeiro are synonyms defined as:

Rio and Rio de Janeiro: the former capital and 2nd largest city of Brazil; chief Brazilian port; famous as a tourist attraction

Rio (noun)	Rio de Janeiro (noun)
the former capital and 2nd largest city of Brazil; chief Brazilian port; famous as a tourist attraction	the former capital and 2nd largest city of Brazil; chief Brazilian port; famous as a tourist attraction