'unattainably' originates from the word 'unattainable', which is derived from the prefix 'un-' meaning 'not', and the word 'attainable', which comes from the Latin 'attingere', meaning 'to reach or touch'.

'unattainable' evolved from the Old French word 'atteindre', which meant 'to reach or achieve', and eventually became the modern English word 'attain'.

Initially, it meant 'not able to be reached or achieved', and this meaning has largely remained the same in modern usage.