Efficacy and Functionality

noun

• Capacity or power to produce a desired effect.
  • usage: "concern about the safety and efficacy of the vaccine"
  • synonyms: efficaciousness

(n.) Power to produce effects; operation or energy of an agent or force; production of the effect intended; as, the efficacy of medicine in counteracting disease; the efficacy of prayer.

noun

• Capable of serving a purpose well.
  • usage: "software with greater functionality"