cops vs policeman

cops

noun
  • The police, considered as a group entity. 

  • The connecting crook of a harrow. 

policeman

noun
  • A male police officer, sometimes used for any police officer regardless of gender. 

  • Any skipper of the genus Coeliades. 

  • A glass rod capped at one end with rubber, used in a chemistry laboratory for gravimetric analysis. 

  • Synonym of enforcer 

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