WordWeb Online

1. Not producing an intended effect
   - ineffective, uneffective
    
2. Producing no result or effect
   "the therapy was ineffectual"
   - futile, otiose, unavailing
    
3. Lacking in power or forcefulness
   "an ineffectual ruler"
   - ineffective, unable, effete

See also: effectiveness, effectivity, effectuality, effectualness, idle, impotent, ineffectually, ineffectualness, inefficacious, inefficient, powerless, toothless, unproductive, useless