The given name is an Anglicised form of the Gaelic Gille Easbaig (also rendered Gilleasbaig), meaning "bishop's servant".
[4] An early example of the name in Scotland occurs in a charter dated 1175–1199, recording a certain "Ewano filio Gillaspeck".
[3][5] In Ireland, a family bearing the surname occupied the office of toísech of Clann Aílebra in the late twelfth century.
[7] Whatever the case, a later family bearing the surname appears on record as erenaghs of Kilraine in County Donegal.
[6] During the nineteenth century in Ireland, the surname was most numerous in the counties of Antrim, Donegal, Armagh, and Tyrone.