Ireland vs Irish Republic

Ireland and Irish Republic both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ireland	Yes	No	No	No
Irish Republic	Yes	No	No	No

As nouns, Ireland and Irish Republic are synonyms defined as:

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

Other synonyms of Ireland include Eire, Republic of Ireland.

Ireland (noun)	Irish Republic (noun)
an island comprising the republic of Ireland and Northern Ireland	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