'impeachability' is formed in modern English from the verb 'impeach' + the suffix '-ability' (from French/Latin origin), where 'impeach' ultimately derives from Old French 'empechier' and '-ability' comes via Old French '-abilite' from Latin.

'impeach' changed from Old French 'empechier' (medieval use) into Middle English 'impechen' and eventually became the modern English verb 'impeach'; the adjectival/nominal suffix '-ability' entered English via Old French '-abilite' and Latin '-abilitas', producing 'impeachability' in modern English.

Initially related to 'hindering' or 'entangling' (Old French sense), 'impeach' later acquired the legal sense 'to accuse (especially a public official)'; 'impeachability' therefore came to mean 'the state of being capable of such an accusation or removal.'