Mammoth Uncensored Word List:
12 words ending with ns, 22 letters long

constitutionalizations counterinterpretations disestablishmentarians overcommercializations overindustrialisations overindustrializations quadragintacentillions quattuortrigintillions quinquanonagintillions quinquaoctogintillions quinquasexagintillions septuagintacentillions