Mammoth Uncensored Word List:
20 - 18 letter words starting with pr

praiseworthinesses preaccommodatingly preacknowledgement preacknowledgments preclassifications predestinarianisms predeterminability prediscriminations premillenarianisms premultiplications preposterousnesses presumptuousnesses presuppositionless pretranscriptional proletarianisation proletarianization pronounceabilities propagandistically propertylessnesses provincializations