croon vs groaning

croon

noun
  • A soft or sentimental hum or song. 

verb
  • To make a continuous hollow moan, as cattle do when in pain. 

  • To say softly or gently 

  • To hum or sing softly or in a sentimental manner. 

  • To soothe by singing softly. 

groaning

noun
  • A low sound associated with extended suffering, sorrow, and toil. 

adj
  • Heavily laden, as if to creak under the strain. 

  • That groans. 

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