iceman vs matricide

iceman

noun
  • An assassin. 

  • One who is cool under pressure. 

  • A human figure carved out of ice. 

  • A man who is skilled in travelling upon ice, as among glaciers. 

  • A person who trades in ice; a person employed to deliver block ice. 

  • An ancient human male mummified in ice. 

matricide

noun
  • A person who kills his or her mother. 

  • The killing of one's mother. 

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