Ó Doineannaigh
Ó DOINEANNAIGH—I—Denanny, Dennany, Dennan; 'descendant of Doineannach' (stormy, tempestuous); originally a midland surname. Ruithin O Doineannaigh, tanist of Teathbha, was slain, according to the Four Masters, in 1044. I cannot find any early anglicised form.
Alphabetical Index to Irish Surnames