faithfulness vs let-down

faithfulness

noun
  • The state of being faithful 

let-down

noun
  • A disappointment or anticlimax. 

  • The clearance of an aircraft to descend through clouds to clear air below, or the process of granting such a clearance. 

  • The neurohormonal release of milk in dairy cows or in breastfeeding human mothers. 

How often have the words faithfulness and let-down occurred in a corpus of books? (source: Google Ngram Viewer )