meth·a·done 
(mĕthə-dōn′)
(mĕthə-dōn′)n.
A potent synthetic narcotic drug, C21H27NO, that is less addictive than morphine or heroin and is used as a substitute for these drugs in addiction treatment programs. It may also be used for chronic pain management.
[Short for methadone hydrochloride : (DI)METH(YL) + A(MINO) + D(IPHENYL) + (heptan)one, a ketone (HEPTAN(E) + -ONE).]