narcotic

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A drug, such as morphine or heroin, that is derived from opium or an opiumlike compound, relieves pain, often induces sleep, can alter consciousness, and is potentially addictive.
• noun A controlled substance.
• noun A soothing, numbing agent or thing.
• adjective Inducing sleep or stupor; causing narcosis.
• adjective Of or relating to narcotics, their effects, or their use.
• adjective Of, relating to, or intended for one addicted to a narcotic.

from The Century Dictionary.

• Having the power to produce stupor.
• Consisting in or characterized by stupor: as, narcotic effects.
• noun A substance which directly induces sleep, allaying sensibility and blunting the senses, and which, in large quantities, produces narcotism or complete insensibility.

from the GNU version of the Collaborative International Dictionary of English.

• adjective (Med.) Having the properties of a narcotic; operating as a narcotic.
• noun (Med.) A drug which, in medicinal doses, generally allays morbid susceptibility, relieves pain, and produces sleep; but which, in poisonous doses, produces stupor, coma, or convulsions, and, when given in sufficient quantity, causes death. The best examples are opium (with morphine), belladonna (with atropine), and conium.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Any class of substances or drugs, that reduces pain, induces sleep and may alter mood or behaviour.
• noun Any type of numbing drug.
• noun Certain illegal drugs.
• adjective Of, or relating to narcotics.
• adjective Inducing sleep; causing narcosis.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective inducing mental lethargy
• adjective of or relating to or designating narcotics
• adjective inducing stupor or narcosis
• noun a drug that produces numbness or stupor; often taken for pleasure or to reduce pain; extensive use can lead to addiction