cops vs peace officer

cops

noun
  • The police, considered as a group entity. 

  • The connecting crook of a harrow. 

peace officer

noun
  • A civil law enforcement officer with a duty to maintain law and order, i.e. bylaw officer, police officer, sheriff, etc. 

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