cognac vs liqueur

cognac

noun
  • A brandy distilled from white wine in the region around Cognac in France. 

liqueur

noun
  • A flavoured alcoholic beverage that is usually very sweet and contains a high percentage of alcohol. 

verb
  • to top up bottles of sparkling wine with a sugar solution 

  • to flavor or treat (wine) with a liqueur 

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