1. Possessing some properties characteristic of opiate narcotics but not derived from opium
2. Of, involving, or induced by an opioid

1. Any of a group of endogenous neural polypeptides (as an endorphin or enkephalin) that bind especially to opiate receptors and mimic some of the pharmacological properties of opiates — called also opioid peptide
2. A synthetic drug possessing narcotic properties similar to opiates but not derived from opium; broadly; opiate