currency vs petty cash

currency

noun
  • Money or other items used to facilitate transactions. 

  • The state of being current; general acceptance or recognition. 

  • Paper money. 

petty cash

noun
  • Cash available for trivial purchases, especially limited funds for employees to use without close supervision. 

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