The mouth. Shut your potatoe trap and give your tongue a holiday; i.e. be silent. IRISH WIT.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Pot Hunter * Pothooks and HangeksNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes