bunk off vs sag off

bunk off

verb
  • To play truant 

sag off

verb
  • Used other than figuratively or idiomatically: see sag, off. 

  • To back off from an opponent against whom one is defending. 

  • To skive; to fail to attend school when required to do so. 

  • To move too far leeward when sailing on the wind. 

  • To fall in share price. 

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