Megistotherium (from Greek, megistos "greatest" + therion "beast" and osteon 'bone' + thlaston 'crushed, bruised' with -es being an agent noun: 'bone-crusher') is an extinct genus of hyaenodontid, the only known species of which is Megistotherium osteothlastes. It is most likely a junior synonym of Hyainailouros sulzeri