metopon
/mɪˈtəʊpɒn/Pharmacology
noun
A narcotic analgesic derived from morphine, usually administered as the hydrochloride; dihydromethylmorphinone, C18H21NO3.
Origin
1940s; earliest use found in Journal of the American Medical Association. Perhaps from met- + -o (in hydro-) + -p- + -on (in -one).