PEEPERS,
a Looking-glass. Track the Dancers and Pike with the Peepers; Whip up the Stairs, and trip off with the Looking-glass.
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Entry taken from 1736 Canting Dictionary, by Nathan Bailey.
Peepers in the 1811 Vulgar Tongue
Also see examples in Canting Songs and Slang Rhymes collected by John S. Farmer (1896).