Green’s Dictionary of Slang

mophead n.

[SE mop + -head sfx (2)]

a derog. term for an inhabitant of Sudan.

[Aus]Morn. Bulletin (Rockhampton, Qld) 19 Apr. 9/8: Much water has passed down the Nile since Kipling paid his tribute to the ‘mop-heads’ whom we encountered in the campagin which went from 1884 to 1888.