severe vs unrelenting

severe

adj
  • Strict or harsh. 

  • Very bad or intense. 

  • Sober, plain in appearance, austere. 

unrelenting

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

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

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