'anesthetically' originates from 'anesthetic', which comes from the Greek word 'anaisthēsia', where 'an-' meant 'without' and 'aisthēsis' meant 'sensation'.

'anaisthēsia' was adopted into English as 'anesthesia', and the adjective 'anesthetic' was formed, with the adverb 'anesthetically' following standard English adverb formation.

Initially, it meant 'without sensation', but over time it evolved into its current meaning of 'in a manner relating to anesthesia or insensitivity to pain'.