The Irish surname Monaghan is an anglicized form of Gaelic Ó Manacháin meaning “descendant of Manachán,” a personal name representing a diminutive of manach meaning “monk.” The Gaelic name is sometimes interpreted as if it were Ó Muineacháin meaning “descendant of the little shrubbery.” The famous annals of Ireland known as 'The Four Masters', apparently record the fact that the O' Monahan clan were the local Lords of Tuathas in County Roscommon upto the year 1287, when they were driven off their lands by the O'Hanlys. The surname is most famous for the number of members who became successful practioners at law, with James Monaghan of Galway (1804-1878) being Attorney General of Ireland.