Mammoth Uncensored Word List:
27 - 11 letter words starting with up

upbraidings upbringings upbuildings upbuoyances upcountries upfollowing upgathering upgradation upgradeable upholstered upholsterer upholstress upliftingly uppercasing uppercrusts upregulated upregulates uprightness upsettingly upspringing upstreaming upstretched upsurgences upthrusting upthundered uptightness upvaluation