down payment vs prepayment

down payment

noun
  • A payment representing a fraction of the price of something being purchased, made to secure the right to continue making payments towards that purchase. 

  • Any initial commitment signifying an intention to carry out a larger future commitment, even though no legal rights or obligations are secured. 

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 down payment and prepayment occurred in a corpus of books? (source: Google Ngram Viewer )