ballad vs carol

ballad

verb
  • To compose or sing ballads. 

noun
  • A slow romantic song. 

  • A kind of narrative poem, adapted for recitation or singing; especially, a sentimental or romantic poem in short stanzas. 

carol

verb
  • To sing in a joyful manner. 

  • To sing carols; especially to sing Christmas carols in a group. 

  • To praise or celebrate in song. 

  • To sing (a song) cheerfully. 

  • To participate in a carol (a round dance accompanied by singing). 

noun
  • A (usually traditional) religious or secular song sung at Christmastime. 

  • A round dance accompanied by singing. 

  • A ballad or song of joy. 

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