accrual vs aggregation

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. 

aggregation

noun
  • The state of being collected into a mass, assemblage, or sum (aggregated). 

  • Summarizing multiple routes into one route. 

  • The act of collecting together (aggregating). 

  • The majority of the parasite population concentrated into a minority of the host population. 

  • Kind of object composition which does not imply ownership. 

  • A collection of particulars; an aggregate. 

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