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From nal(or)phine + (cyclo)bu(tyl).
Etymology from Wiktionary, CC BY-SA 4.0.
nalbuphine
Today it means: A synthetic opioid antagonist which is very similar to morphine in chemical structure and is given by injection (usually in the form of its hydrochloride) as an analgesic; (−)-(5R,6S,14S)-9a-cyclobutylmethyl-4,5-epoxymorphinan-3,6,14-triol, C₂₁H₂₇NO₄. Full definition →