WordWeb Online

1. Power to be effective; the quality of being able to bring about an effect
   - effectivity, effectualness, effectuality
    
2. Capacity to produce strong physiological or chemical effects
   "the toxin's effectiveness";
   - potency, strength

See also: effective, effectual, efficacious, impotent, ineffective, ineffectual, potent, stiff, strong, uneffective

Type of: power, powerfulness

Antonym: ineffectiveness

Encyclopedia: Effectiveness