Origin of the name Brennan:

Transferred use of the surname, which is from the Irish O Brennan, the Anglicized form of the Gaelic Ó Braonáin (descendant of Braoin). Braoin is a Gaelic name meaning “sorrow, saddness.” Brennan is also an English surname and is evolved from the Old English Burnand (burned hand). The name makes reference to the medieval practice of burning the hands of those caught breaking the law. Var: Brennand, Brennen.

From A World of Baby Names by Teresa Norman.Buy the book