To MELT,
to spend Money. Will you melt a Borde? Will you spend your Shilling? The Cull melted a Couple of Decusses upon us; The Gentleman spent Ten Shillings upon us.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
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To Melt in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).