The head. I fired into her keel upwards; my eyes and limbs Jack, the crown office was full; I s—k-d a woman with her a—e upwards, she was so drunk, that her head lay on the ground.
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.
Crow Fair * CruisersNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes