A fetter. Double slanged; double ironed. Now double slanged into the cells for a crop he is knocked down; he is double ironed in the condemned cells, and ordered to be hanged.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Slamkin * Slang-1Nathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes