SCRAP,
s Design, a purpos'd Villainy, a vile Intention; also a perpetrated Roguery: He whiddles the whole Scrap: He discovers all he knows.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Scrap in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).