Cuba vs Republic of Cuba

Cuba and Republic of Cuba both are nouns.

Word	Noun	Adjective	Verb	Adverb
Cuba	Yes	No	No	No
Republic of Cuba	Yes	No	No	No

As nouns, Cuba and Republic of Cuba are synonyms defined as:

Cuba and Republic of Cuba: a communist state in the Caribbean on the island of Cuba

Cuba (noun)	Republic of Cuba (noun)
a communist state in the Caribbean on the island of Cuba	a communist state in the Caribbean on the island of Cuba
the largest island in the West Indies