Ó Donnacháin
Ó DONNACHÁIN—I—O Donaghan, O Duneghan, O Dunchan, Doonican, Dunican, Duncan; 'descendant of Donnachán' (diminutive of donn, brown); apparently a variant of Ó Donnagáin, which see. See also Ó Duinneacháin.
Alphabetical Index to Irish Surnames