settle down vs shack up

settle down

verb
  • To establish a settled lifestyle, and especially to marry. 

  • To get comfortable with one's new accommodation or circumstances. 

  • To become quiet and calm after a period of disturbance or restlessness. 

shack up

verb
  • To live together, especially of an unmarried couple. 

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