croon vs singalong

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. 

singalong

noun
  • A gathering of people who sing together 

adj
  • designed to allow or encourage the audience to sing along 

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