Originally an Anglicized form of the ancient Irish male name Ceallach. It is now very widely used in the English-speaking world, mainly as a girl's name. This is a transferred use of the surname Ó Ceallaigh ‘descendant of Ceallach’.
Irish: shortened Anglicized form of Gaelic Ó hAnluain ‘descendant of Anluan’, a personal name from the intensive prefix an- + luan ‘light’, ‘radiance’ or ‘warrior’. Occasionally Hanlon has been used to represent Hallinan.