Mammoth Uncensored Word List:
50 words ending with on, 19 letters long

antidesertification autotransplantation bronchoconstriction conventionalization countermobilization crossclassification cytodifferentiation deepithelialization dehydrochlorination deindividualization deindustrialisation deindustrialization departmentalisation departmentalization homotransplantation hypersophistication immunoprecipitation intellectualization interstratification macrostratification microstratification mischaracterization nonagintacentillion nondisqualification octogintacentillion overdifferentiation overdiversification overintensification overprocrastination overrationalization phacoemulsification photodisintegration photointerpretation photopolymerization professionalisation professionalization quinquavigintillion radiopasteurization reconceptualisation reconceptualization reindustrialization septentrigintillion sexagintacentillion superspecialization ultracentrifugation ultrapasteurization underrepresentation unquinquagintillion unviginticentillion xenotransplantation