Ryan (Irish: Ó Riain) is a common surname of Irish origin, as well as being a common given name in the English-speaking world.
There are several different origins for the surname. In some cases it may be a shortened form of O'Ryan, which is an Anglicized adaptation of the Gaelic surname Ó Riain, meaning "descendant of Rian".[1] It can also be a shortened form of Mulryan or O'Mulryan, which are derived from the Gaelic Ó Maoilriain, meaning "descendant of the follower of Rian".[1][2]
The meaning of the Old Irish name Rian is unknown.[3] Some sources have suggested that it is related to the Old Irish word rían, meaning "water" or "ocean".[4][5] Others have suggested that it is related to the Old Irish word rí, meaning "king".[6][7] Both of these etymologies have been discounted by scholars, however.[3] According to John Ryan, Professor of Early and Medieval History at University College Dublin, "What the Rian in the surnames Ó Riain and Ó Maolriain is has never been satisfactorily explained. Rian, like Niall, seems to be so ancient that its meaning was lost before records began."[3]
Popular modern sources typically suggest that Ryan means "little king"[8][9] or "illustrious".[2][10]
There are also cases in which Ryan is an Americanized form of the German surname Rein.[1]