Which country's name would apparently come from Irish meaning "descendant"?

The irish word for descendant is "O" which prefixes many irish surnames.
As the question is in the Literature and Arts trivia,the only possibility I can think of is Brazil.
Brazil is a ghost Island used in many Irish myths. The name comes from the irish "Uí Breasail" or "O Breasail" which means descendants of Breasal an ancient irish clan.
It has been said the the South American country was named after this mythical place.
Viv

Very good Viv. Source