merciless vs stern

merciless

adj
  • Showing no mercy; cruel and pitiless. 

stern

adj
  • Grim and forbidding in appearance. 

  • Having a hardness and severity of nature or manner. 

verb
  • To propel or move backward or stern-first in the water. 

noun
  • A bird, the black tern. 

  • The tail of an animal; now used only of the tail of a dog. 

  • The hinder part of anything. 

  • The post of management or direction. 

  • The rear part or after end of a ship or vessel. 

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