Source : Webster's Revised Unabridged Dictionary (1913)

Megathere \Meg"a*there\, Megatherium \Meg`a*the"ri*um\, n. [NL.
   megatherium, fr. Gr. me`gas great + thyri`on beast.]
   (Paleon.)
   An extinct gigantic quaternary mammal, allied to the
   ant-eaters and sloths. Its remains are found in South
   America.

Source : WordNet®

megathere
     n : gigantic extinct terrestrial sloth-like mammal of the
         Pliocene and Pleistocene in America [syn: {ground sloth}]