What is the meaning of the word "nail down"?

Definitions:

  1. To confirm or settle something with certainty, often used in the context of finalizing plans or agreements. copy to clipboard VERB
    • We need to nail down the details of the project before moving forward. copy to clipboard
  2. To fasten or hold something securely, often by using nails. copy to clipboard VERB
    • They nailed down the loose floorboards. copy to clipboard

Synonyms: