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

• particle physics
• particolored
• particolored buckeye
• particoloured
• particular
• Particular Baptist
• particular date
• particular proposition
• particularisation
• particularise
• particularised
• particularism
• particularist
• particularistic
• particularity
• particularization
• particularize
• particularized
• particularly
• particulate
• particulate matter
• particulate radiation
• parting
• parting shot
• partisan