Longman Dictionary of Contemporary English homepage

efficacy

noun
     
ef‧fi‧ca‧cy [uncountable + of]
formal the ability of something to produce the right result [= effectiveness]

Dictionary pictures of the day
Do you know what each of these is called?
What is the word for picture 1? What is the word for picture 2? What is the word for picture 3? What is the word for picture 4?
Click on any of the pictures above to find out what it is called.

Explore our topic dictionary