abridge vs slack up

abridge

verb
  • Cut short; truncate. 

  • To make shorter; to shorten in duration or extent. 

  • To shorten or contract by using fewer words, yet retaining the sense; to epitomize; to condense. 

  • To curtail. 

slack up

How often have the words abridge and slack up occurred in a corpus of books? (source: Google Ngram Viewer )