To humbug. To deceive, To tell lies. What rum gamon the old file pitched to the flat; how finely the knowing old fellow humbugged the fool.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Game-1 * Gamon and PatterNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes