Mammoth Uncensored Word List:
18 - 17 letter words starting with he

headmistressships hemagglutinations hemangioblastomas hematopoietically hemiachromatopsia hemichromatopsias hemilaminectomies hemispherectomies hemochromatosises hemoconcentration hemodiafiltration heptapentagesimal heterogeneousness heteronormativity heterosexualities heterotrophically hexachloroethanes hexapentagesimals