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

"There's a term called 'RuneScapiness' which is a little bit hard to nail down," game designer Molly Mason told the BBC.

From BBC

Sivakumar spent much of October talking to entrepreneurs to nail down an investment.

From The Wall Street Journal

There’s fun to be had in there, and Nintendo has that category nailed down.

From Barron's

In between fits of laughter and finishing each other’s sentences, the members explain that they’d recently come back from a European press tour and only had a week to nail down their tour performance.

From Los Angeles Times

Clarke said he poured over recordings of the trial, listening to them first before he watched the videos, partly as a way to nail down the specificities of Alex’s accent and cadence.

From Los Angeles Times