nail down

verb

nailed down; nailing down; nails down

1

: to make (something, such as a victory) certain to happen

They need to score another touchdown to nail down the victory.

2

: to find out or identify (something) exactly

Her doctors haven't yet been able to nail down a diagnosis.

They're trying to nail down the cause of our network problems.

3

: to make (something) definite or final

nail down a decision