Murphy

Irish: Anglicized form of Gaelic Ó Murchadha 'descendant of Murchadh', a personal name composed of the elements muir 'sea' + cath 'battle', i.e. 'sea-warrior'. This was an important family in Tyrone.

he surname is a variant of two Irish surnames: "Ó Murchadha"/"Ó Murchadh" (descendant of "Murchadh"), and "Mac Murchaidh"/"Mac Murchadh" (son of "Murchadh") derived from the Irish personal name "Murchadh", which meant sea-warrior or sea-battler (muir meaning sea and cath meaning battle).

It is said of Murrough (Murchadh) as he entered the thick of the fight and prepared to assail the foreign invaders, the Danes, when they had repulsed the Dal-Cais, that 'he was seized with a boiling terrible anger, an excessive elevation and greatness of spirit and mind. A bird of valour and championship rose in him, and fluttered over his head and on his breath.

In modern Irish, "Ó Murchú", rather than "Ó Murchadha", is used.

"Murphy" is the most common surname in Ireland, the fourteenth most common surname in Northern Ireland, and the fifty-eighth most common surname in the United States.