sag off vs sluff

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. 

sluff

verb
  • ignore, shrug (off) 

  • To play truant from (school). 

  • to avoid working 

noun
  • An avalanche, mudslide, or a like slumping of material or debris. 

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