Recorded in several spellings including Monaghan, Monahan, and more properly O'Monahan, and sometimes Monk, although this is also an English name, this is an Irish surname of great antiquity. It derives from the pre 10th century Gaelic word 'manachain' meaning a monk. However it would seem that the first chief from whom all later nameholders descended, was perhaps both monk and a mighty warrior of the 9th century. A case of mistaken identity or something more sinister? The history book are silent, but as we know from the famous tales of Robin Hood, the Friar was not above a little swordsmanship when the necessity arose. 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. Certainly the surname is very popular in Galway, Fermanagh and Mayo, to the west, and it is certainly a truism of Irish history that under both national and local pressure as in this case, native tribes tendered to move west when in trouble. 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, and later Lord Chief Justice.`