expletive vs headword

expletive

noun
  • A word that adds to the strength of a phrase without affecting its meaning. 

  • A profane, vulgar term, notably a curse or obscene oath. 

  • A word without meaning added to fill a syntactic position. 

adj
  • Serving to fill up, merely for effect, otherwise redundant. 

  • Marked by expletives (phrase-fillers). 

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. 

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