DUP,
to enter, or open a Door: Dup the Ken, Enter the House. Dup the Boozing Ken and booz a Gage, Go into the Ale-house and drink a Pot.
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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).