indifference vs unconcern

indifference

noun
  • Unemotional apathy. 

  • Unconcerned nonchalance. 

  • The state of being indifferent. 

  • Unbiased impartiality. 

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

  • A lack of enthusiasm. 

unconcern

noun
  • Lack of interest or care; indifference or apathy. 

  • Freedom from worry or apprehensiveness; insouciance or nonchalance. 

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