n. a synthetic opioid analgesic that has approximately half the pain-control efficacy of codeine. It was generally marketed in combination with a nonsteroidal anti-inflammatory agent, such as aspirin, for the management of moderate pain. In 2010, it was withdrawn from the U.S. market due to its risk of causing potentially fatal arrhythmia. Former U.S. trade names: Darvocet (in combination with acetaminophen); Darvon.