pigeon-hearted vs poltroon

pigeon-hearted

adj

  • timid; easily frightened; chicken-hearted 

poltroon

adj

  • Cowardly. 

noun

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

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