To cheat. Let us bilk the rattling cove; let us cheat the hackney coachman of his fare. Cant. Bilking a coachman, a box-keeper, and a poor whore, were formerly, among men of the town, thought gallant actions.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Bilboa * Bill of SaleNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes