[2][3][4] Historically, one source of the surname was the prominent clan Ua Braonáin (O'Brennan) of Uí Duach (Idough)[5] in Osraige who were a junior Dál Birn sept stemming from a younger son of Cerball mac Dúnlainge (d.888).
[6] Recent surname evaluations highlighted the geographic consistency of this lineage in the barony of Idough.
[7][8] However, based on the ultimate authority of Dubhaltach Mac Fhirbhisigh they are out of Ui Dhuinn (O’Dunn)[9] and, therefore, an Uí Failghi tribe, not Osraige.
While it is clearly apparent that O’Hart's pedigree is erroneous, it is suggested that Ó Cléirigh probably became confused while transcribing from Mac Fhirbhisigh.
The Irish surname Ó Branáin, means "descendant of Branán".