fade out vs slacken

fade out

verb
  • To slowly disappear. 

  • To fade from a cut to black in a movie. 

  • To decrease in volume, such as at the end of a song, until there is only silence. 

noun
  • A type of transition used in film, usually at the end of a scene, involving a fade to black from the cut. 

slacken

verb
  • To gradually decrease in intensity or tautness; to become slack. 

  • To make slack, less taut, or less intense. 

  • To deprive of cohesion by combining chemically with water; to slake. 

How often have the words fade out and slacken occurred in a corpus of books? (source: Google Ngram Viewer )