Mammoth Uncensored Word List:
28 words ending with ps, 15 letters long

accountantships ambassadorships apprenticeships archpriestships bipartisanships catechumenships chancellorships commandantships commissaryships consultantships controllerships councillorships counsellorships goodfellowships headmasterships instructorships legislatorships licentiateships lieutenantships magistrateships postmasterships procuratorships progenitorships prolocutorships proprietorships stadholderships supercargoships supervisorships