Masterson, Mac an Máighistir
An English surname meaning son of the Master (a reference to a cleric). There is also a Scottish surname of similar derivation, from Dumfries and Wigstown. Mac an Mháighistir a sept of Breffny, who originated in Cavan has been so anglicised. In 1890 the surname was principally found in Dublin, Longford and Cavan, and the estimated number of bearers was 2,100.