pachyderm

from WordNet (r) 3.0 (2006)

pachyderm
    n 1: any of various nonruminant hoofed mammals having very thick
         skin: elephant; rhinoceros; hippopotamus

from The Collaborative International Dictionary of English v.0.48

pachyderm \pach"y*derm\ (p[a^]k"[i^]*d[~e]rm), n. [Cf. F.
   pachyderme.] (Zool.)
   Any of various nonruminant hoofed mammals having very thick
   skin, including the {elephant}, {rhinoceros}, and
   {hippopotamus}, one of the Pachydermata.
   [WordNet 1.5 + 1913 Webster]