Ó Manannáin
Ó MANANNÁIN—I—O Manynane, O Mananan, Marrinan, Murnane, &c.; 'descendant of Manannán' (the name of an ancient Irish sea-god); an old Thomond surname; now found chiefly in East Limerick, Tipperary, Cork, and parts of Leinster, but long corrupted to Ó Marannáin, Ó Marnáin, Ó Murnáin, and Ó Manaráin, which see.
Alphabetical Index to Irish Surnames