regrettable vs unacceptable

regrettable

adj
  • Able to be regretted, especially deserving of regret. 

unacceptable

adj
  • not conforming to accepted usage 

  • unsatisfactory; not acceptable 

noun
  • Something that is not acceptable. 

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