From an Irish surname, an Anglicized form of Ó Fionnagáin meaning "descendant of Fionnagán". The name Fionnagán is a diminutive of Fionn. This was the name of a character in James Joyce's novel 'Finnegans Wake' (1939), the title of which was based on a 19th-century Irish ballad called 'Finnegan's Wake'.