unrelenting vs yielding

unrelenting

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

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

yielding

adj
  • Docile, or inclined to give way to pressure. 

noun
  • A concession. 

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