flesher vs mass murderer

flesher

noun

  • A butcher. 

  • A person who removes the flesh from the skin during the making of leather. 

  • A tool used to remove the flesh from the skin during the making of leather. 

mass murderer

noun

  • Someone who commits a mass murder. 

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