come to an end vs slacken off

come to an end

verb
  • To stop; to cease; to no longer continue. 

slacken off

verb
  • To do (something) less intensely. 

  • To slacken or lessen; to become less intense. 

How often have the words come to an end and slacken off occurred in a corpus of books? (source: Google Ngram Viewer )