NAB,
a Hat, Cap, or Head, also a Coxcomb. Ill nab ye, I'll have your Hat or Cap. Nim the Nab, steal the Hat or Cap. Nabbed, apprehended, taken or arrested.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Nab in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).