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: Webster's Revised Unabridged Dictionary (1913)