From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) A disease of the skin, in which it become enormously thickened, and is rough, hard, and fissured, like an elephant's hide.

The Nuttall Encyclopedia [2]

A peculiar skin disease, accompanied with abnormal swelling; so called because the skin becomes hard and stiff like an elephant's hide; attacks the lower limbs and scrotum; is chiefly confined to India and other tropical countries.