In the practice of medicine, especially surgery, and dentistry, anesthesia or anaesthesia (from Greek ἀν-, an-, "without"; and αἴσθησις, aisthēsis, "sensation"; see American and British English spelling differences) is an induced, temporary state with one or more of the following characteristics: analgesia (relief from or prevention of pain), paralysis (extreme muscle relaxation), amnesia (loss of memory), and unconsciousness. An anesthetic is an agent that causes anaesthesia.