slack off vs slummock

slack off

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

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

slummock

verb
  • To behave lazily or indolently 

  • To behave awkwardly or clumsily 

noun
  • A slovenly person 

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