megatherePalæont.|ˈmɛgəθɪə(r)| Anglicized form of megatherium. 1839Owen in Trans.Geol.Soc. (1842) VI. 93 The external cuneiform bone of the Megathere differs [etc.].1887Sir H. H. Howorth Mammoth & Flood 346 Great mylodons and thickly-hided megatheres.