ditty vs tag line

ditty

noun
  • A saying or utterance, especially one that is short and frequently repeated. 

  • A short, simple verse or song. 

verb
  • To sing; to warble a little tune. 

tag line

noun
  • Synonym of dialogue tag 

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