Old Peg; poor hard Suffolk or Yorkshire cheese. A peg is also a blow with a straightarm: a term used by the professors of gymnastic arts. A peg in the day-light, the victualling office, or the haltering-place; a blow in the eye, stomach, or under the ear.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Peery * Peg Trantum’sNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes