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

---

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]

---

Example Sentences

If one had to nail down the central theme of “The Audacity,” aside from pure human foible, it would be the perils posed to privacy by the profitability of data.

From The Wall Street Journal • Apr. 9, 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

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

"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