ballad vs rune

ballad

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

  • A slow romantic song. 

verb
  • To compose or sing ballads. 

rune

noun
  • A verse or song, especially one with mystical or mysterious overtones; a spell or an incantation. 

  • A letter, or character, used in the written language of various ancient Germanic peoples, especially the Scandinavians and the Anglo-Saxons. 

  • A Finnish or Scandinavian epic poem, or a division of one, especially a division of the Kalevala. 

  • A letter or mark used as a mystical or magic symbol. 

  • A Unicode code point. 

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