Mammoth Uncensored Word List:
14 words ending with as, 17 letters long

bromomenorrhagias bronchopneumonias cholangiosarcomas chondrodysplasias counterguerrillas fibromyxosarcomas hemangioblastomas hemichromatopsias oligoastrocytomas pheochromocytomas pseudoparenchymas rhabdomyosarcomas thrombocytopenias trichotillomanias