Ó Clothacháin
Ó CLOTHACHÁIN—I—O Cloghane, Clogan, (Callaghan); 'descendant of Clothachán' (diminutive of clothach, famous); the name of an old ecclesiastical family the head of which was 'steward of St. Patrick' in Munster, now anglicised Clogan in Co. Limerick. It appears to be the same as the name which is pronounced Ó Colacháin in West Clare and anglicised Callaghan.
Alphabetical Index to Irish Surnames