Great-grandfather is "Sin-seanathair".
The Irish for "great-grandfather" is "sinseanathair";I've never heard a nickname for it, although a nickname for "grandfather" is "daideo".In Irish it's "gar athair"
His great grandfather was Irish on the Kennedy side, and his grandfather on the Fitzgerald side.
If your great great great great great grandfather was from Ireland and none of your ancestors in other lines were Irish, then you would be said to be 1/128th Irish. But no one bothers with such small fractions.
sinseanathair
sin-seanathair
Great is a separate word and grandfather is one word great grandfather or great great grandfather
If your great great great grandfather was your only ancestor from Ireland then you would be 1/32 Irish since you have 32 great great great grandparents. That would be slightly more than 3%.
To say "great grandfather" with 11 greats, write the word "great" eleven times and then write the word "grandfather." Some people say "eleventh great grandfather."
The Yiddish word for great-grandfather is "גרויספאָפֿער" (groysfoper).
She was African-American, Cherokee-Creek, and Scottish-Irish ancestry. Her great grandfather was Scottish-Irish.
"Abuelo" is a grandfather and "Abuela" is a grandmother
seanathair is the more formal word but you can also say daideo