roper vs shamus

roper

noun
  • Synonym of outside man (“accomplice who locates a mark to be swindled by a confidence trickster”) 

  • One who ropes goods; a packer. 

  • An undercover informer. 

  • Any of a variety of monsters with tentacles that they use to capture victims. 

  • A person hired by a gambling establishment to locate potential customers and bring them in. 

shamus

noun
  • A private detective; originally, a policeman or police detective. 

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