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 • Mar. 26, 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

Instead, nail down the parts that are boring.

From Barron's • Feb. 7, 2026

"But with Hubble's Advanced Camera for Surveys, we're able to nail down that there's nothing there."

From Science Daily • Jan. 9, 2026

Vincent hopes to finally nail down drawing the human figure.

From "Vincent and Theo: The Van Gogh Brothers" by Deborah Heiligman