The story
Reduced Anglicized form of either of two Irish surnames, Ó Duibhín (“descendant of Duibhín”), a byname from a hypocoristic form of dubh (“black”), or Ó Daimhín (“descendant of Daimhín”), a byname from a hypocoristic form of damh (“stag”).
Etymology from Wiktionary, CC BY-SA 4.0.