Pachyderma: Thick skin, like that of a pachyderm (an elephant, rhinoceros, or hippopotamus). The adjective is pachydermatous. Pachyderma can occur in several medical conditions, such as chronic lymphedema.
From the Greek pachydermos meaning "thick skin" from pachys meaning "thick" + derma meaning "skin."
REFERENCE: Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.