A spying glass; also a looking-glass. Track up the dancers, and pike with the peeper; whip up stairs, and run off with the looking-glass. Cant.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
To Peel * PeepersNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes