Ó Breaslain is a Gaelic-Irish surname, the anglicised form of which is Breslin. The epynom, Breisel, lived in the 10th/11th century, his name meaning violent, truculent. There were two families of the name in Tyrconnell (now County Donegal).
Read more about Breslin: Uí Breaslain Cenél Enda, Uí Breaslain Fánaid, Others of The Name, Buildings