indifference vs slackness

indifference

noun
  • The state of being indifferent. 

  • Unconcerned nonchalance. 

  • Unbiased impartiality. 

  • Unemotional apathy. 

  • Self-identity defined through the negation of difference, non-difference. 

  • A lack of enthusiasm. 

slackness

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

  • A subgenre of dancehall music with sexual lyrics. 

  • Vulgarity in West Indian culture. 

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