Green’s Dictionary of Slang

(Anglo-Ind.) a resident of the Madras Presidency.

1816		‘Quiz’ Grand Master 145: A well-known Mul. popp’d out his head. [footnote: An abbreviation for Mulkatany, a common appellation for Madras officers.
1828		[C. D’Oyly] Tom Raw 21: ‘Qui hi?’ [...] has become a bantering designation of residents of Bengal, as ‘Mull,’ abbreviation of mullagatanee (pepper-water), of those at Madras.