anesthesia (n.) Look up anesthesia at
1721, "loss of feeling," medical Latin, from Greek anaisthesia "want of feeling or perception, lack of sensation (to pleasure or pain)," abstract noun from an- "without" (see an- (1)) + aisthesis "feeling," from PIE root *au- (4) "to perceive" (see audience). 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.