ability vs skill set

ability

noun
  • A skill or competence in doing; mental power; talent; aptitude. 

  • A unique power of the mind; a faculty. 

  • The quality or state of being able; capacity to do or of doing something; having the necessary power. 

  • Physical power. 

  • The legal wherewithal to act. 

skill set

noun
  • The skills needed to accomplish a specified task or perform a given function. 

  • A set of skills. 

How often have the words ability and skill set occurred in a corpus of books? (source: Google Ngram Viewer )