'questionability' is formed from the noun 'question' plus the nominalizing suffix '-ability' (from Latin-derived '-abilitas'), indicating 'the state or quality of being question(ed)'.

'question' comes from Old French 'question' (from Latin 'quaestio'), itself from the verb 'quaerere' meaning 'to seek, ask'. The abstract suffix '-ability' comes via Old French/Latin '-abilitas'; combining them produced 'questionability' in modern English to denote the state of being questionable.

Initially related to the act of asking or seeking ('question' from Latin 'quaestio'), the compound came to denote the state of being open to doubt or challenge—i.e., 'susceptibility to doubt' in modern usage.