Mammoth Uncensored Word List:
34 - 19 letter words starting with u

ultracentrifugation ultracontemporaries ultrafundamentalist ultrapasteurization ultrasegregationist ultratraditionalist unaccommodatingness unapprehendableness unapproachabilities unauthoritativeness unceremoniousnesses uncommunicativeness uncompartmentalized uncompartmentalizes uncompetitivenesses unconscientiousness unconscionabilities unconstitutionality uncontrollabilities unconventionalities undecicentillionths undemonstrativeness underrepresentation understandabilities unexceptionableness unfashionablenesses unidimensionalities unintelligibilities unpretentiousnesses unquinquagintillion unsexagintillionths untranslatabilities unviginticentillion uvulopalatoplasties