The surname (O) Daly (and its variants Daily, Daley etc.) is Ó Dalaigh in Irish, deriving from Dálach meaning "one who is present at assemblies"; the root word is Dáil, now the official title of the parliament of the Republic of Ireland. A connection is possible between the meaning of the name and the long tradition of scholarship and poetic achievement associated with those who bear it, since the ollamh of Gaelic Ireland had a place of honour at the tribal dail as a man of learning and a poet.
The medieval genealogists derived the family from the southern Uí Neill, part of the great tribal grouping that also produced the O'Donnells and the O'Neills, and located their homeland in the present Co. Westmeath. Cuchonnacht Ó Dalaigh, head of a famous bardic school in neighbouring Meath, is the first clearly historical individual to appear in these genealogies. He died in 1139, and his grandson Aengus is credited as the progenitor of the various branches of the family, which spread throughout the country by acting as ollamhs to the most prominent families - the MacCarthys of Munster, the O'Connors of Connacht, the O'Byrnes of Leinster, the O'Loughlins of Clare and many others.
Although the Westmeath origin of the surname is best known, from a very early date families of the name were prominent in Co. Cork, and especially in the area around the peninsula of Muintervarra or Sheep's Head in west Cork. The likeliest explanation is that the name had a separate origin in the south. Even so, the O'Dalys of Desmond had an equally strong association with poetry and learning: so potent were the poems of Aonghus Ó Dalaigh of Ballyroon that he was murdered by one of the victims of his satires.
In modern times, too, the surname has been associated with learning and scholarship. Cearbhall Ó Dalaigh, fifth President of Ireland, was a man of wide learning and culture, a linguist and Chief Justice of the Supreme Court. The current Roman Catholic Primate of All Ireland, Cardinal Cathal Daly, is also a distinguished scholar.
The widespread growth of the family is seen today in the fact that Daly is among the twenty-five most common surnames in the country. It is now estimated that almost 17000 individuals carry the name in Ireland, with the greatest concentrations in the south and west, and in Co. Westmeath.
The arms of the family reflect the mythology surrounding its origins. The royal emblem of the lion probably derives from King Conaire, regarded as the family's human ancestor in prehistory, with the red hands coming from the name of Conaire's palace Bruidhin da derg, the fortress of the red god or goddess. Curoi Mac Daire, the reputed divine ancestor of the Dalys, provides the crest, from Cu, meaning "hound", and Dair, meaning "oak-tree", both sacred in the old pre-Christian religion.