Mammoth Uncensored Word List:
26 words ending with s, 23 letters long

antiestablishmentarians carboxymethylcelluloses chemoorganoheterotrophs dacryocystorhinostomies deinstitutionalizations duoquinquagintillionths friggatriskaidekaphobes hexamethylenetetramines indistinguishablenesses intersubstitutabilities microspectrophotometers nonillionsedecillionths nonrepresentationalisms paraskavedekatriaphobes paraskevidekatriaphobes psychoneuroimmunologies quattuorvigintillionths quinquagintacentillions quinquanonagintilliards quinquaoctogintilliards quinquasexagintilliards quinquatrigintillionths quinquavigintilliardths reinstitutionalizations sesquinquagintillionths unquinquagintilliardths