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.
sin-seanathair
sinseanathair
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.
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