Estonia vs Republic of Estonia

Estonia and Republic of Estonia both are nouns.

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

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

Estonia and Republic of Estonia: a republic in northeastern Europe on the Baltic Sea, with capital Tallinn

Other synonyms of Estonia include Esthonia.

Estonia (noun)	Republic of Estonia (noun)
a republic in northeastern Europe on the Baltic Sea, with capital Tallinn	a republic in northeastern Europe on the Baltic Sea, with capital Tallinn