nail down

British  

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

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nail down Idioms  

1. 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]

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Example Sentences

Their numbers are hard to nail down, but in the first half of 2025, nearly 4 in 10 new vehicle registrations were hybrid and EV variants.

From Los Angeles Times

When Rupert’s children watched its too-close-for-comfort version of the chaos following Logan Roy’s sudden death, they leapt to nail down their family’s succession plan before it was too late.

From Salon

The seasonal aspect of food was nailed down for me in L.A.

From Los Angeles Times

The death toll in Iran has been difficult to nail down, but Iran’s ambassador to the U.N. on Friday put the number at more than 1,300.

From Los Angeles Times

EU-Swiss ties are currently governed by a patchwork of agreements, and the two have for years been striving to nail down a broader cooperation agreement.

From Barron's