frosting vs gratuity

frosting

noun
  • Icing, a sweet, often creamy and thick, covering for cakes and other baked goods. 

  • A layer of frost. 

  • The theft of a car while it is left unattended, especially when its engine is left running in the winter to defrost the car. 

gratuity

noun
  • An additional payment given freely as thanks for service. 

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