Mammoth Uncensored Word List:
63 words ending with on, 18 letters long

antiadministration antidiscrimination bourgeoisification chlorofluorocarbon counterinstitution counterreformation counterretaliation crossfertilisation crossfertilization disproportionation electrocoagulation electrodesiccation evapotranspiration grammaticalization hyperconcentration hypersensitization intercommunication medicalexamination microencapsulation neovascularization nondifferentiation nondiversification nonstandardization noventrigintillion operationalisation operationalization overcapitalisation overcapitalization overcentralisation overcentralization overclassification overgeneralisation overgeneralization overidentification overinterpretation overneutralization overrepresentation oversimplification overspecialisation overspecialization photodecomposition photoisomerisation photoisomerization photosensitisation photosensitization polyesterification postmultiplication proletarianisation proletarianization radiosensitization sentimentalisation sentimentalization septemvigintillion subminiaturization supersensitisation supersensitization territorialization transmogrification transubstantiation trigintacentillion undersocialisation underspecification xenotransplanation