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

She gave them until early May to nail down a plan, otherwise they’d stick with the existing part.

From The Wall Street Journal • May 5, 2026

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 • Mar. 14, 2026

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 • Mar. 8, 2026

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 • Feb. 25, 2026

I was hoping last night would be a success and that I’d be able to nail down the location of the Flash and who the boy is.

From "Split the Sky" by Marie Arnold