What is Anesthetic?

Legal Definition
An anesthetic (or anaesthetic) is a drug to prevent pain during surgery. A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside of anesthesia, although others are used commonly by all disciplines. Anesthetics are categorized into two classes: general anesthetics, which cause a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body while maintaining consciousness. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Adverse effects, however, may also be increased.
-- Wikipedia
Legal Definition
A drug that causes loss of sensation. This loss can be total or partial. If overexposed side effects can occur and even death in severe cases.