Brennan

The story

1. Irish · borrowed fromÓ Branáin“descendant of Branán”
2. Irish · borrowed fromÓ Braonáin“descendant of Braonán”
3. English todayBrennan

From Irish Ó Braonáin (“descendant of Braonán”), a diminutive of braon (“moisture, drop”). Alternatively, from Irish Ó Branáin (“descendant of Branán”), a diminutive of bran (“raven”).