Morphine: A powerful narcotic agent that has strong analgesic (pain relief) action and other significant effects on the central nervous system. It is dangerously addicting. Morphine is a naturally occurring member of a large chemical class of compounds called alkaloids. The name, which derives from Morpheus (the mythologic god of dreams) was coined in 1805 by German apothecary Adolf Serturner to designate the main alkaloid in opium. Opium comes from the poppy plant.