'inattentively' originates from the Latin word 'inattentus', where 'in-' meant 'not' and 'attentus' meant 'attentive'.

'inattentus' transformed into the Old French word 'inattentif', and eventually became the modern English word 'inattentive', with 'inattentively' as its adverbial form.

Initially, it meant 'not paying attention', and this meaning has largely remained the same in modern usage.