Mammoth Uncensored Word List:
15 words that are 20 letters long beginning with h in the mammoth uncensored word list.

histocompatibilities histomorphologically homotransplantations hydrochlorothiazides hydrodesulfurization hydrometallurgically hyperadrenocorticism hypercholesterolemia hypercholesterolemic hypercoagulabilities hyperconsciousnesses hyperdolichocephalic hyperparathyroidisms hypersensitivenesses hypersynchronousness