noun (n)

• power to be effective; the quality of being able to bring about an effect

  kekuatan untuk lebih berkesan; kualitas mampu membawa tentang efek

  Synonym:
  effectivity, effectuality, effectualness
  Antonym:
  ineffectiveness, ineffectuality, ineffectualness
  

  source: wordnet30
• capacity to produce strong physiological or chemical effects

  kapasitas untuk menghasilkan kesan kuat fisiologi atau kimia

  Synonym:
  potency, strength
  

  source: wordnet30
• The quality of being effective.

  kualiti menjadi efektif.

  source: webster1913