unmollifiable vs unrelenting

unmollifiable

adj
  • That cannot be mollified. 

unrelenting

adj
  • Not relenting; not yielding in strength, severity, or determination. 

  • Having no pity; not being or becoming lenient, mild, gentle, or merciful 

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