Where does “Ó Grianáin” come from?

Ó Grianáin (Irish) comes from Irish Ó, from Irish ua, from Old Irish áue, from Primitive Irish ᚐᚃᚔ, from Proto-Celtic awyos, from Proto-Indo-European h₂ewh₂yos — grandfather.

Ancestry of “Ó Grianáin”, step by step

Ó Grianáin traces back through two separate lines of ancestry.

via Irish Ó

Step	Language	Word	Meaning
1	Irish	Ó	Alternative form of ó used in surnames
2	Irish	ua	Archaic form of ó
3	Old Irish	áue	grandson
4	Primitive Irish	ᚐᚃᚔ	descendant
5	Proto-Celtic	awyos	—
6	Proto-Indo-European	h₂ewh₂yos	grandfather

via Irish grianán

Step	Language	Word	Meaning
1	Irish	grianán	solar sunny upstairs room
2	Old Irish	gríanán	a sunny place, a bower, a place open to the sun
3	Old Irish	-án	diminutive suffix
4	Primitive Irish	-ᚐᚌᚅᚔ	diminutive suffix
5	Proto-Celtic	*-agnos	—

Every word from Proto-Indo-European h₂ewh₂yos →Every word from Proto-Celtic awyos →Every word from Primitive Irish ᚐᚃᚔ →