inefficacy (n.)youdaoicibaDictYouDict[inefficacy 词源字典]
"want of force or virtue to produce the desired effect," 1610s, from Late Latin inefficacia, from inefficacem (nominative inefficax), from in- "not, opposite of" (see in- (1)) + efficax (see efficacy).[inefficacy etymology, inefficacy origin, 英语词源]