Shannon Family History

reduced form of Shanahan. reduced Anglicized form of Gaelic Ó Seanáin ‘descendant of Seanán’, a personal name based on a pet form of seán ‘old’. in County Clare, a reduced Anglicized form of Mac Giolla tSeanáin ‘son of the servant of St. Seanán’. In the Irish midlands Leonard and Nugent have been adopted as equivalents of this name.

Source: Dictionary of American Family Names ©2013, Oxford University Press