Английский словарь американских идиом - nail down

{v. phr.}, {informal} To make certain; make sure; settle. * /Joe had a hard time selling his car, but he finally nailed the sale down when he got his friend Sam to give him $300./ * /The New York Yankees nailed down the American League Championship when they beat the Red Sox 3 to 0 on September 1 5./