The word for one of medicine's greatest discoveries was proposed in a private letter, about five weeks after the discovery itself.
On 16 October 1846, the dentist William Morton gave ether vapor to Gilbert Abbott, a surgical patient of Dr. John Collins Warren, at Massachusetts General Hospital in Boston. Morton called his preparation "Letheon" and refused at first to say what was in it. Henry J. Bigelow published an account of the cases in the Boston Medical and Surgical Journal on 18 November.
Three days later, on 21 November, the Boston doctor Oliver Wendell Holmes Sr. wrote to Morton. He suggested calling the new state "anæsthesia," which, he wrote, "signifies insensibility, more particularly (as used by Linnaeus and Cullen) to objects of touch." The matching adjective would be "anæsthetic." He considered and rejected anatomical coinages such as "neuro-leptic." He also predicted that the terms would be "repeated by the tongues of every civilized race of mankind."
Holmes did not invent the word. Etymonline dates anesthesia in English to 1721, meaning a loss of feeling, borrowed from medical Latin. Behind that sits the Greek anaisthesia, "want of feeling or perception." It joins an-, "without," to aisthesis, "feeling," from an Indo-European root meaning "to perceive." What Holmes did was give an old diagnostic term a new job, naming a state that doctors could now produce on purpose.
The new sense took hold quickly. Etymonline dates the surgical meaning to 1846. It credits the noun anesthetic, for the agent itself, to the Scottish doctor James Young Simpson in 1848, a pioneer of chloroform. Holmes's letter had already floated an "anæsthetic agent," so the two accounts overlap.
The Greek root has a surprising sibling. Aesthetic comes from aisthetikos, "of or for perception by the senses." The German philosopher Alexander Baumgarten bent it in the 1750s toward judging taste and beauty. So anesthesia and aesthetics share a root. One is the absence of sensation, and the other began as the study of it.