perseverance vs slackness

perseverance

noun
  • Continuing in a course of action without regard to discouragement, opposition or previous failure. 

slackness

noun
  • A subgenre of dancehall music with sexual lyrics. 

  • The state of being slack; the quality of having slack. 

  • Vulgarity in West Indian culture. 

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