casualness vs unconcern

casualness

noun
  • A relaxed and nonchalant attitude. 

  • The state of being casual. 

unconcern

noun
  • Freedom from worry or apprehensiveness; insouciance or nonchalance. 

  • Lack of interest or care; indifference or apathy. 

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