anaesthesia

n. (Pathology) lack of feeling, loss of sensation (caused by disease); (Medicine) localized or general reduction of sensitivity to pain (through drugs)

Anesthesia or anaesthesia (see spelling differences; from Greek αν- an- “without” + αἲσθησις aisthesis “sensation”) has traditionally meant the condition of having the feeling of pain and other sensations blocked. This allows patients to undergo surgery and other procedures without the distress and pain they would otherwise experience. The word was coined by Oliver Wendell Holmes, Sr. in 1846. Another definition is a "reversible lack of awareness", whether this is a total lack of awareness (e.g. a general anaesthestic) or a lack of awareness of a part of a the body such as a spinal anaesthetic or another nerve block would cause.
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Anesthesia /an·es·the·sia/ 1. loss of sensation, usually by damage to a nerve or receptor. 2. loss of the ability to feel pain, caused by [more]Anaesthesia - Community and Resources

(n.)
Entire or partial loss or absence of feeling or sensation; a state of general or local insensibility produced by disease or by the inhalation or application of an anaesthetic.
  

anaesthesia or US noun
loss of the feeling of pain
epidural anaesthesia = local anaesthesia (used in childbirth) in which anaesthetic is injected into the space between the vertebral canal and the dura mater
general anaesthesia = loss of feeling and loss of consciousness
local anaesthesia = loss of feeling in a certain part of the body
spinal anaesthesia = local anaesthesia in which an anaesthetic is injected into the cerebrospinal fluid

US = ANAESTHESIA