anesthesia (n.) Look up anesthesia at Dictionary.com
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- "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.