buydown vs prepayment

buydown

noun
  • An accelerated repayment of the principal of a loan. 

  • A payment by a third-party to a lender to reduce some of all of the payments otherwise required, especially in first few years of the loan, thereby enhancing the apparent quality of the loan. 

prepayment

noun
  • A payment in advance. 

  • An asset recognized in respect an expense incurred in a period for which the benefit will be received in a future period. 

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