set out vs slope off

set out

verb
  • To go out, leave. 

  • To explain something, or give exact details, usually in writing. 

  • To position, to put in a position 

  • To start an activity with the intention of finishing it. 

slope off

verb
  • To depart quietly, without being noticed. 

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