apropos vs regardless

apropos

adj
  • Of an appropriate or pertinent nature. 

  • by the way, incidental 

adv
  • To the purpose; appropriately. 

  • By the way. 

  • Timely; at a good time. 

prep
  • Regarding or concerning. 

regardless

adj
  • Having no regard; heedless; careless. 

  • despite everything; despite the situation 

prep
  • Synonym of regardless of; paying no attention to 

adv
  • Without attention to warnings or indications of bad consequences. 

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