The meaning of "nail someone down" is:
The definition of "nail someone down" is:
make sure someone won’t break up with you by marrying them
A: How’s your girlfriend?
B: Great! She’s beautiful, smart, funny, rich and she cooks like my mother.
A: When are you going to nail her down then?
B: When she takes some cooking classes. My mother is a horrible cook.
After 5 years of dating, he finally nailed her down and proposed to her.
Media and Links: