happy hour vs interregnum

happy hour

noun
  • A time of day, usually in the afternoon or early evening, when a bar or pub offers its drinks at a discounted price. 

  • Any small gathering, usually in the afternoon or early evening, set aside to relax and have a drink. 

  • Flowers. 

interregnum

noun
  • The period of time between the end of a sovereign's reign and the accession of another sovereign. 

  • A period of time during which normal executive leadership is suspended or interrupted. 

  • An intermission in any order of succession; any breach of continuity in action or influence. 

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