effectual,
efficacious,
effective marked by qualities giving the power to produce an intended effect; "written propaganda is less efficacious than the habits and prejudices...of the readers"-Aldous Huxley; "the medicine is efficacious in stopping a cough"
idle not in active use; "the machinery sat idle during the strike"; "idle hands"
inefficacious lacking the power to produce a desired effect; "laws that are inefficacious in stopping crime"
inefficient not producing desired results; wasteful; "an inefficient campaign against drugs"; "outdated and inefficient design and methods"
impotent lacking power or ability; "Technology without morality is barbarous; morality without technology is impotent"- Freeman J.Dyson; "felt impotent rage"
ineffective -
lacking the ability or skill to perform effectively; inadequate; "an ineffective administration"; "inefficient workers"
