Mammoth Uncensored Word List:
21 words ending with n, 20 letters long

adrenocorticotrophin anthropomorphization compartmentalisation compartmentalization counterdemonstration duoquinquagintillion electrogalvanization endophotocoagulation hydrodesulfurization institutionalisation institutionalization internationalisation internationalization microminiaturization nonillionsedecillion photophosphorylation piezocrystallization pseudosophistication quattuorvigintillion quinquatrigintillion sesquinquagintillion