The arm. The busnapper’s kenchin seized my rammer; i.e. the watchman laid hold of my arm. Cant.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Rammish * To RampNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes