cops vs plod

cops

noun
  • The police, considered as a group entity. 

  • The connecting crook of a harrow. 

plod

noun
  • the police, police officers 

  • A slow or labored walk or other motion or activity. 

  • a police officer, especially a low-ranking one. 

verb
  • To walk or move slowly and heavily or laboriously (+ on, through, over). 

  • To toil; to drudge; especially, to study laboriously and patiently. 

  • To trudge over or through. 

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