'assessability' originates from English, formed from the adjective 'assessable' plus the suffix '-ity'. The verb 'assess' ultimately traces back to Medieval Latin 'assessare', itself from Latin 'assidere' (ad- meaning 'to' + sedēre meaning 'to sit').

'assess' changed from Medieval Latin 'assessare' into Old French forms such as 'assesser' and into Middle English forms like 'assessen' before becoming modern English 'assess'. From 'assess' came 'assessable' (with the suffix '-able') and later 'assessability' (with the further nominalizing suffix '-ity').

Initially connected with the idea 'to sit beside' (a literal sense of sitting as an assessor), the verb shifted to the specialized sense 'to determine value or amount'; over time this extended to abstract nouns such as 'assessability' meaning 'the quality of being able to be assessed'.