slush fund vs sweetener

slush fund

noun
  • Money that has not been hypothecated or dedicated to a particular purpose, or which is used for a different purpose than originally intended. 

  • Money stored for illegal or dishonest purposes. 

sweetener

noun
  • Something given or added to added to a deal to sweeten another's attitude, especially a bribe or kickback. 

  • A shill bidder at an auction. 

  • Something added to food to sweeten its taste, especially an artificial substitute for sugar. 

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