accrual vs cumulation

accrual

noun
  • An increase; something that accumulates, especially an amount of money that periodically accumulates for a specific purpose 

  • from the creditor's viewpoint, a charge incurred in one accounting period that has not been, but is to be, paid by the end of it. 

cumulation

noun
  • Accumulation. 

  • The effect of free trade agreements on the rules of origin in calculating importation tariffs, quotas, etc. 

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