pachyderm

Concise Oxford English Dictionary © 2008 Oxford University Press:
pachyderm /ˈpakɪdəːm/

▶noun a very large mammal with thick skin, especially an elephant, rhinoceros, or hippopotamus.

– derivatives
pachydermal adjective,
pachydermatous adjective.

– origin C19: from Fr. pachyderme, from Gk pakhudermos, from pakhus ‘thick’ + derma ‘skin’.