O'Callaghan (/əˈkæləhən,oʊ-,-hæn,-ɡən,-ɡæn/[1][2]) or simply Callaghan without the prefix (anglicized from two separate surnames and clans, Ó Ceallacháin, Munster Clan. Ó Ceileacháin, Oriel Clan) is an Irish surname.
^Wells, John C. (2008), Longman Pronunciation Dictionary (3rd ed.), Longman, p. 557, ISBN9781405881180
^Jones, Daniel (2003) [1917], Peter Roach; James Hartmann; Jane Setter (eds.), English Pronouncing Dictionary, Cambridge: Cambridge University Press, ISBN3-12-539683-2