1721, "loss of feeling," medical Latin, from Greek anaisthēsia "want of feeling or perception, lack of sensation (to pleasure or pain)," abstract noun from an- "without" (see an- (1)) + aisthēsis "feeling," from PIE root *au- "to perceive." For the abstract noun ending, see -ia. As "a procedure for the prevention of pain in surgical operations," from 1846. Aesthesia "capacity for feeling" is attested in English from 1853, perhaps a back-formation.
<a href="https://www.etymonline.com/word/anaesthesia">Etymology of anaesthesia by etymonline</a>
Harper, D. (n.d.). Etymology of anaesthesia. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/anaesthesia