ouster UK /ˈaʊstə/US /ˈʌʊstəɹ/noun 4verb 1forms 3 noun4 •Action by a cotenant that prevents another cotenant from enjoying the use of jointly owned property. •A putting out of possession; dispossession; ejection. •(US) The forceful removal of a politician or regime from power; a coup; an ousting.Mr. [Rishi] Sunak, a former chancellor whose resignation in July precipitated Mr. [Boris] Johnson’s ouster, earlier said he would not serve in Ms. [Liz] Truss’s cabinet. — 2022 •Someone who ousts. verb1 •To oust. formsoustered · oustering · ousters