Green’s Dictionary of Slang

commissioner n.

[? ironic use of commissioner of Newmarket Heath n., given the role of Newmarket in racing and the bookmaker’s extraction of money from his clients]

the properietor of a gaming house, a bookmaker.

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[UK]Sporting Mag. May XXIV 124/1: The first, and of the greatest importance, is the commissioner, always a proprietor [of a casino] who looks in at night.