Rio de Janeiro vs Rio

Rio de Janeiro and Rio both are nouns.

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

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

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

Rio de Janeiro (noun)	Rio (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