abend vs let up

abend

verb
  • To terminate abnormally. 

noun
  • The abnormal termination of a program. 

  • Termination of a process prior to completion. 

let up

verb
  • To cease or stop. 

  • To cease or stop (doing something intense). 

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