RUM-Clank,
a large Silver Tankard. Tip me a Rum-Clank of Bowse; i.e. Give me a Double-tankard of Drink.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
The Vulgar Tongue originally collected by Grose, 1811.
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).