Ó Duibhdhíorma
Ó DUIBHDHÍORMA, Ó DUIBHDHÍORMAIGH—I—O Dughierma, Dooyearma, Dyermott, Diarmod, Dermott, Dermond, (O'Dermott, MacDermott), &c.; 'descendant of Dubhdhíorma(ch)' (black-trooper); the name of a family of Cinel Eoghain who were anciently lords of Bredach, which comprised the eastern half of Inishowen, and are still numerous in Donegal; often shortened to Ó Díorma, and anglicised MacDermott.
Alphabetical Index to Irish Surnames