'asininity' originates from Latin, specifically the word 'asinus', where 'asinus' meant 'ass' or 'donkey'. The English adjective 'asinine' came from Latin 'asininus' ('pertaining to a donkey'), and 'asininity' was formed by adding the noun-forming suffix '-ity' to 'asinine'.

'asininity' changed from the adjective 'asinine' (from Latin 'asininus' via Middle English/French influences) and eventually became the noun 'asininity' in modern English through the addition of '-ity' to indicate a state or quality.

Initially it related to donkey-like characteristics (literally 'of a donkey' or figuratively 'stubborn'), but over time 'asinine' came to mean 'stupid' or 'foolish', and 'asininity' evolved to mean 'the quality or instance of being foolish'.