sluggard vs yellow back

sluggard

noun
  • A fearful or cowardly person, a poltroon. 

  • A person who is lazy, stupid, or idle by habit. 

  • A person slow to begin necessary work, a slothful person. 

yellow back

noun
  • A coward. 

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