loll vs slack off

loll

verb
  • To act lazily or indolently while reclining; to lean; to lie at ease. 

  • To let (the tongue) hang from the mouth in this way. 

  • To hang extended from the mouth, like the tongue of an animal heated from exertion. 

slack off

verb
  • To decrease in intensity; to ease off; to diminish; to die down. 

  • To be deliberately unproductive in one's work or study. 

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