From second half of XIII century, found in central-southern varieties.
Borrowed from Franco-Provençal pota (“protruded lips, pout”), probably a rebracketing of *lippotte, diminutive of French lippe (“protruded lip”), from Middle Dutch lippe (“lip”), from Proto-Indo-European *leb- (“to droop, sag, slip”). For the derogatory sense, cf. English cunt and twat.