ace in the hole vs backing

ace in the hole

noun
  • Synonym of ace up one's sleeve 

backing

adj
  • Providing support for the main performer. 

noun
  • Support, especially financial. 

  • A backdrop. 

  • The mounting of a horse or other animal. 

  • The action of putting something back; a switching into reverse. 

  • A liner or other material added behind or underneath. 

  • Musicians and vocalists who support the main performer. 

How often have the words ace in the hole and backing occurred in a corpus of books? (source: Google Ngram Viewer )