Where does “Eire” come from?

Éire derives from Old Irish Ériu, from Proto-Celtic ɸīweryū, ultimately from Proto-Indo-European peyH-, a root of uncertain meaning.

Ancestry of “Eire”, step by step

Step	Language	Word	Meaning
1	Irish	Éire	Ireland
2	Old Irish	Ériu	Ireland
3	Primitive Irish	*Īweriū	—
4	Proto-Celtic	Φīweryū	—
5	Proto-Indo-European	piHweryon-	—
6	Proto-Indo-European	peyH-	fat, milk

Eire — Etymology, Origin & Word History | Etymology Explorer