Eire vs Republic of Ireland

Eire and Republic of Ireland both are nouns.

Word	Noun	Adjective	Verb	Adverb
Eire	Yes	No	No	No
Republic of Ireland	Yes	No	No	No

As nouns, Eire and Republic of Ireland are synonyms defined as:

Eire and Republic of Ireland: a republic consisting of 26 of 32 counties comprising the island of Ireland; achieved independence from the United Kingdom in 1921

Other synonyms of Eire include Ireland, Irish Republic.

Eire (noun)	Republic of Ireland (noun)
a republic consisting of 26 of 32 counties comprising the island of Ireland; achieved independence from the United Kingdom in 1921	a republic consisting of 26 of 32 counties comprising the island of Ireland; achieved independence from the United Kingdom in 1921