nail down

verb

1. to fasten down with or as if with nails
2. informal.
   to extort a definite promise or consent from

   I nailed him down on the deadline

3. informal.
   to settle in a definite way

   they nailed down the agreement

Idioms and Phrases

Establish conclusively, as in The reporter nailed down the story by checking all the facts . This metaphoric expression alludes to fixing or fastening something down with nails. [c. 1600]

Example Sentences

"No-one has been able to nail down who exactly has benefited. It’s almost like a beer parlour gossip about who is getting what," says Toyin Akinosho of the Africa Oil+Gas Report.

From BBC

I nailed down the fastest, safest route home from my job in Westwood.

From Los Angeles Times

“Right now the U.S. consumer is buying everything that isn’t nailed down,” said Rupkey.

From Los Angeles Times

So perhaps expecting it to be nailed down for 90 minutes just three games in is just not realistic.

From BBC

It can take a while to get through the process and nail down a contractor — who may have trouble getting supplies, causing further delays.

From Salon