Mammoth Uncensored Word List:
15 words that are 26 letters long in the mammoth uncensored word list.

esophagogastroduodenoscopy octillionduotrigintillions psychoneuroimmunologically quinquagintacentilliardths quinquagintaducentilliards quinquagintaducentillionth quinquagintatrecentilliard quinquagintatrecentillions quinquaquadragintilliardth quinquaquadragintillionths quinquaquinquagintilliards quinquaquinquagintillionth quinquaseptuagintilliardth quinquaseptuagintillionths undecillionsedecilliardths