RUM-Cull,
a rich Fool, that can be easily bit, or cheated by any body; also one that is very generous and kind to a Mistress.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Rum Cull in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).