headword vs riff

headword

noun
  • Any word which may be modified by an adjunct. 

  • A word used as the title of a section, particularly in a dictionary, encyclopedia, or thesaurus. 

riff

noun
  • A variation on something. 

  • A spoof. 

  • A clever or witty remark. 

  • Listen to one of the greatest guitar riffs of all time! 

  • A repeated instrumental melody line in a song. 

verb
  • To improvise in the performance or practice of an art, especially by expanding on or making novel use of traditional themes. 

  • To riffle. 

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