noun Biochemistry, Pharmacology.
- any opiumlike substance.
- any of a group of natural substances, as the endorphins, produced by the body in increased amounts in response to stress and pain.
- any of several synthetic compounds, as methadone, having effects similar to natural opium alkaloids and their derivatives.
- pertaining to such a substance.
- any of a group of substances that resemble morphine in their physiological or pharmacological effects, esp in their pain-relieving properties
- (modifier)of or relating to such substancesopioid receptor; opioid analgesic
n.1957, from opium + -oid. n.