Mammoth Uncensored Word List:
10 words that are 28 letters long in the mammoth uncensored word list.

antidisestablishmentarianism chemoorganoheterotrophically ethylenediaminetetraacetates hexakosioihexekontahexaphobe octillionduotrigintillionths pharyngolaryngoesophagectomy quinquagintaducentilliardths quinquagintatrecentilliardth quinquagintatrecentillionths quinquaquinquagintilliardths