The Collaborative International Dictionary of English v.0.48:
Megathere \Meg"a*there\, Megatherium \Meg`a*the"ri*um\, n. [NL. megatherium, fr. Gr. me`gas great + qhri`on beast.] (Paleon.) An extinct gigantic quaternary mammal, allied to the ant-eaters and sloths. Its remains are found in South America. [1913 Webster]WordNet (r) 3.0 (2006):
Megatherium n 1: type genus of the Megatheriidae [syn: Megatherium, genus Megatherium]