Brennan (surname)

Brennan is an Irish surname which is an Anglicised form of two different Irish language surnames—Ó Braonáin and Ó Branáin. Historically, one source of the surname was the prominent clan Ua Braonáin (O'Brennan) of Uí Duach (Idough) in Osraige who were a junior Dál Birn sept stemming from a younger son of Cerball mac Dúnlainge (d.888). Recent surname evaluations highlighted the geographic consistency of this lineage in the barony of Idough.

The Gaelic surname Ó Braonáin, means "descendant of Braonán". The personal name Braonán is derived from a word which means "moisture", "drop". The Gaelic surname Ó Branáin, means "descendant of Branán". The personal name Branán means "little raven".Brennan is also a given name.

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