handfast vs shack up

handfast

verb
  • To betroth by joining hands, in order to allow for cohabitation before the celebration of marriage; to marry provisionally. 

  • To pledge; to bind. 

adj
  • Strong; steadfast. 

shack up

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

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