Recorded as O'Cahill, MacCahill, McCahill, Cahill and possibly others, this is a famous Irish surname. Whether originally O' or Mac prefix, it derives from the pre 10th century Olde Gaelic name Cathail. When it occurs the prefix 'O' indicates 'the male descendant of' and Mac, the son of, whilst Cathail is from the pre 6th century Celtic elements 'catu-valus' meaning 'battle powerful'. The O'Cahills originally hailed from County Galway, but by the early 13th century their place had been taken by the O' Shaughnessys and the original members divided into several individual and much smaller septs which eventually secured lands in the Munster counties of Clare, Tipperary, Cork, and Kerry. Three townlands called Ballycahill exist in County Tipperary which show that the clan still possessed considerable power even when divided. The first element of the townland name comes from 'baile', and pronounced 'bally' meaning 'the place of'. The MacCahill's are from Counties Donegal and Cavan, but are originally thought to be all the same clan. Amongst the famous name holders In the 17th century the name often lost both the O' and Mac prefix. A good example being Father Daniel Cahill (1796-1864). He was a newspaper editor who lectured extensively in the United States in the cause of Irish Independance. The first recorded spelling of the family name is shown to be that of Flan O' Cahill. This is dated 938a.d. in the Ancient Registers of Ireland, during the reign of Siol Chuinn, King of Ireland and a descendant of 'Conn of the Hundred Battles'. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.