fade away vs prolong

fade away

verb
  • To lose strength, become weaker; to wane; to disappear or reduce slowly. 

noun
  • A technique of painting young women, by having their clothes fade into the background. 

prolong

verb
  • To become longer; lengthen. 

  • To lengthen in time; to extend the duration of 

  • To put off to a distant time; to postpone. 

  • To extend in space or length. 

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