Ó Breisleáin was the surname of an Irish brehon family.
The Ó Breisleáin were natives of Fanad, County Donegal, and a branch of the family later became brehons to the Maguire of County Fermanagh
The surname is now anglicised as Breslin.
References
Ó Breisleáin Wikipedia(Text) CC BY-SA