Ó Lonagáin
Ó LONAGÁIN—I—O Lonagan, O Lonegan, O Lanegane, O Lannegan, Lanigan, Lannigan, &c.; probably 'descendant of Lonagán' (diminutive of lon, a blackbird; compare with lonán), but the origin is not quite clear. O'Donovan thought it might be a corruption of Ó Longacháin; and Ó Fhlannagáin is not an unlikely origin. Also Ó Luineagáin, which see.
Alphabetical Index to Irish Surnames