megalonyx

from The Collaborative International Dictionary of English v.0.48

Megalonyx \Meg`a*lon"yx\, n. [NL., from Gr. me`gas, mega`lh,
   great + 'o`nyx claw.] (Paleon.)
   An extinct quaternary mammal, of great size, allied to the
   sloth.
   [1913 Webster]