commonly pronounced BIDDY. A kind of tub, contrived for ladies to wash themselves, for which purpose they bestride it like a French poney, or post-horse, called in French bidets.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
biddy * bienlyNathan Bailey's 1721 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes