pom-pom vs pompon

pom-pom

noun
  • A rapid-firing small-calibre cannon used especially as an anti-aircraft gun. 

pompon

noun
  • A hardy garden chrysanthemum with button-like flower heads. 

  • A bundle of yarn, string, ribbon, etc. tied in the middle and left loose at the ends, so as to form a puff or ball, as for decoration or a showy prop for cheerleading. 

  • Any of several dwarf varieties of the Provence rose. 

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