Mammoth Uncensored Word List:
32 - 18 letter words starting with r

radiochromatograms radioimmunotherapy radiosensitivities radiosensitization radiosymmetrically rambunctiousnesses rechromatographies rechromatographing reconstructionisms reconstructionists recrystallizations redistributionists rehospitalizations reinstitutionalize remunerativenesses renationalizations reprehensibilities representationally representativeness representativities resynchronisations resynchronizations retransplantations retroreflectometer revascularizations rhabdomyosarcomata rhinolaryngologist rhinolaryngoscopes ribonucleoproteins roentgenologically roentgenopaqueness roentgenotherapies