- an opiate, or any similar synthetic compound: formerly referring only to the latter, but now the predominant term for both the opium-derived and synthetically produced substances: Illicit use of the synthetic opioid fentanyl is on the rise.The opium poppy is the source for all natural opioids.
- any opiumlike substance: Have any opioids been detected in poppies that do not contain opium?
- any of a group of natural substances, as the endorphins, produced by the body in increased amounts in response to stress and pain.
- pertaining to such a substance: opioid drugs such as heroin and oxycodone;opioid neuropeptides.
- any of a group of substances that resemble morphine in their physiological or pharmacological effects, esp in their pain-relieving properties
- of or relating to such substances
