cold fish vs pitiless

cold fish

noun
  • A heartless individual; a person lacking empathy and emotion. 

  • A sexual partner who, during sex, lacks vigor or emotional reciprocity. 

pitiless

adj
  • having no kindly feelings; unkind 

  • having, or showing, no pity; merciless, ruthless 

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