Mac Casey, O’ Casey, Ó Cathasaigh
Ó Cathasaigh comes from “Cathasach”, meaning ‘vigilant in war’. There were several distinct septs of Ó Cathasaigh; in Dublin, Limerick, Cork, Mayo and Roscomon. Today, the name is ranked as 59th most numerous in Ireland, and is found predominantly in the southern province of Munster. One of the most famous bearers of the name was the Irish playwright Seán O’ Casey.