Save Type Surname (from given name) Usage Irish Pronounced Pron. Gill-Day [key] Other Forms FormsMac Giolla Dhé (Gaelic) Gilday, Kilday Meaning & History shortened Anglicized form of Gaelic Mac Giolla Dhé "son of the servant of God" from dia "God". The name originated with a monastic family in Donegal in the 11th century.