Dictionary.net

Originally, agents that caused somnolence or induced sleep; now, any derivative, natural or synthetic, of opium or morphine or any substance that has their effects. Narcotics have potent analgesic effects associated with significant changes in mood and behavior, and with the potential for dependence and tolerance following repeated administration. (Stedman, 25th ed)

term given to a group of drugs that includes morphine and heroin that reduce pain and produce sleep or stupor.

Same etymon. Substances, which have the property of stupefying;- as opium, stramonium, hyoscyamus, belladonna, &c. They are used in medicine as soothing agents; exerting their special influence on the brain and tubular matter of the spinal marrow. In small doses, as a general rule, narcotics stimulate; in large, they act as sedatives. The following is a list of the chief narcotics :-Aconitum, Aetherea, Belladonna, Camphora, Cannabis, Conium, Digitalis, Humulus, Hyoscyamus, Lactucarium, Opium and Morphia, Stramonii Folia, Stramonii Semina, Mental Narcotics. (Appropriate Musio, Monotonous sounds, or any succession of monotonous impressions.)

[Gr.] (Med.) Hypnotics; soporific medicines, diminishing the action of the nervous system, relieving pain, and producing sleep.