anaesthetic

adj. (Medicine) serving to reduce the ability to feel pain, of or pertaining to reducing sensitivity to pain (of drugs); (Pathology) causing lack of feeling (of a disease)

n. substance which reduces sensitivity to pain (i.e. ether or halothane)

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]Anaesthetic - Community and Resources

Noun
1. a drug that causes temporary loss of bodily sensations
(synonym) anesthetic, anesthetic agent, anaesthetic agent
(hypernym) drug
(hyponym) general anesthetic, general anaesthetic
(derivation) anesthetize, anaesthetize, anesthetise, anaesthetise, put to sleep, put under, put out
Adjective
1. characterized by insensibility; "the young girls are in a state of possession--blind and deaf and anesthetic"; "an anesthetic state"
(synonym) anesthetic(a), anaesthetic(a)
(similar) insensible

(n.)
That which produces insensibility to pain, as chloroform, ether, etc.
  

(a.)
Characterized by, or connected with, insensibility; as, an anaesthetic effect or operation.
  

(a.)
Capable of rendering insensible; as, anaesthetic agents.