A cheating bully, or one in a set of gamblers, whose office is to bully any pigeon, who, suspecting roguery, refuses to pay what he has lost. Cant.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
See also the definition in Nathan Bailey's 1736 dictionary of canting and thieving slang.
Captain Queernabs * Captain TomNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes