pigeon-livered vs poltroon

pigeon-livered

adj

  • cowardly 

poltroon

adj

  • Cowardly. 

noun

  • An ignoble or total coward; a dastard; a mean-spirited wretch. 

How often have the words pigeon-livered and poltroon occurred in a corpus of books? (source: Google Ngram Viewer )