Save Type Surname (from given name) Usage Irish (Anglicized) Meaning & History Irish anglicized form of Gaelic Ó Ciaráin ‘descendant of Ciarán’, a byname from a diminutive of ciar ‘dark’, ‘black-haired’. It was borne by two Irish saints, a hermit of the 5th century and the founder of the monastery at Clonmacnoise.