Anesthesia comes from the Greek word anaisthēsia, from an- ‘without’ + aisthēsis ‘sensation’.  It originated from the Greek adjective anesthetos,and later passed as a loan word into other languages, such as modern Latin.  Anaesthetos is a compound word an negative + aesthesis “without feeling, senseless.” 

The first public demonstration of anesthesia in surgery, using ether, took place at Massachusetts General Hospital in Boston on October 16m 1846.  This event, led by dentist William T.G. Morton (1819-1868) and surgeon John Collin Warren (1778-1856), marked the beginning of modern anesthesia. The first documented use of a gas for surgical pain relief, while previously performed by Crawford W. Long, was attributed to William Morton due to his later publication, according to Xenon Health.   It was first used in England on Saturday, December 19, 1846, by a London dentist, James Robinson, who demonstrated the administration of the anesthetic gas ether.  During the American Civil War approximately 95% of surgeries used either chloroform or ether to provide a needed level of pain relief that made battlefield surgery more manageable for both the surgeons and patients. 

However, descriptions of anesthesia based on mixtures of medicinal herbs have been found in manuscripts dating from before Roman times until well into the Middle Ages.  Before the development of modern anesthesia in the 1840s, surgeons relied on a variety of methods to reduce pain and enable patients to endure surgery. These included intoxicants, sedatives, and even substances like opium, alcohol, and herbal concoction "dwale."  Some cultures also used coca leaves and inhalations of various substances like cannabis and mandrake. 

Examples of "anesthesia" used in a sentence:  
"Maybe the numbness is the body providing temporary anesthesia for the pain."
"Patients have many fears regarding surgery, including fear of death, anesthesia, and pain."
"Body piercing is traditionally done without any anesthesia to dull the pain." 
"Dorothy was a ward nurse and trained in the use of anesthesia." 
"The patient was given intravenous medication to induce anesthesia." 
"Awareness during anesthesia is a serious complication with potential long-term psychological consequences." 
"We often radiograph dogs when they are under anesthesia for spaying or neutering or other routine procedures." 

Just the facts:

ANESTHESIA Definition & Meaning - Merriam-Webster