From Irish Gaelic

From the Old Irish name Finn, derived from finn meaning "white, blessed". It occurs frequently in Irish history and legends, the most noteworthy bearer being Fionn mac Cumhaill, the central character of one of the four main cycles of Irish mythology, the Fenian Cycle. Fionn was born as Deimne, and acquired his nickname because of his fair hair. He grew all-wise by eating an enchanted salmon, and later became the leader of the Fianna after defeating the fire-breathing demon Áillen. He was the father of Oisín and grandfather of Oscar.