WordWeb Online

1. Not producing an intended effect
   "an ineffective teacher"; "ineffective legislation"
   - uneffective, ineffectual
    
2. Lacking in power or forcefulness
   - ineffectual, unable, effete
    
3. Lacking the ability or skill to perform effectively; inadequate
   "an ineffective administration"
   - inefficient

See also: effectiveness, effectivity, effectuality, effectualness, idle, impotent, incompetent, ineffectively, ineffectiveness, inefficacious, inefficient, powerless, toothless, unproductive, useless

Antonym: effective