Shanahan, ó Seanacháin A Gaelic surname derived from seanach meaning ‘old, wise’. A sept of the Dál gCais who were chiefs of Ui Rongaile (co-extensive with the parishes of Kilnoe and Killuran in Clare) in Thomond. In 1318 they were expelled by Torlough O’Brien and the MacNamaras. They settled firstly in Waterford, but subsequently scattered. In 1890 Shanahan was principally found in Cork, Kerry, Tipperary, Limerick and Waterford, and the estimated number of bearers was 2,910 (including variants). In the United States Shanahan is the 4,816th most numerous surname with an estimated 5,500 bearers.
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