apology vs palliation

apology

noun
  • A formal justification, defence. 

  • An expression of remorse or regret for having said or done something that harmed another: an instance of apologizing (saying that one is sorry). 

  • Anything provided as a substitute; a makeshift. 

palliation

noun
  • Extenuation; mitigation. 

  • The alleviation of a disease's symptoms without a cure; temporary relief. 

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