craven vs pigeon-livered

craven

adj

  • Unwilling to fight; lacking even the rudiments of courage; extremely cowardly. 

verb

  • To make craven. 

noun

  • A coward. 

pigeon-livered

adj

  • cowardly 

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