"nail down" meaning in English

{
  "forms": [
    {
      "form": "nails down",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "nailing down",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "nailed down",
      "tags": [
        "participle",
        "past"
      ]
    },
    {
      "form": "nailed down",
      "tags": [
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "*"
      },
      "expansion": "nail down (third-person singular simple present nails down, present participle nailing down, simple past and past participle nailed down)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [],
      "examples": [
        {
          "text": "Nail down the shelf, then paint it."
        }
      ],
      "glosses": [
        "to attach with nails"
      ],
      "id": "en-nail_down-en-verb-Rdh6EVvP",
      "links": [
        [
          "nail",
          "nail"
        ]
      ],
      "raw_glosses": [
        "(transitive) to attach with nails"
      ],
      "related": [
        {
          "_dis1": "100 0",
          "word": "copperfasten"
        },
        {
          "_dis1": "100 0",
          "word": "pin down"
        }
      ],
      "tags": [
        "transitive"
      ]
    },
    {
      "categories": [
        {
          "_dis": "35 65",
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        },
        {
          "_dis": "28 72",
          "kind": "other",
          "name": "English phrasal verbs with particle (down)",
          "parents": [],
          "source": "w+disamb"
        },
        {
          "_dis": "28 72",
          "kind": "topical",
          "langcode": "en",
          "name": "Construction",
          "orig": "en:Construction",
          "parents": [
            "Architecture",
            "Engineering",
            "Applied sciences",
            "Art",
            "Technology",
            "Sciences",
            "Culture",
            "All topics",
            "Society",
            "Fundamental"
          ],
          "source": "w+disamb"
        }
      ],
      "examples": [
        {
          "text": "They haven't nailed down their vacation plans yet."
        }
      ],
      "glosses": [
        "to make something (e.g. a decision or plan) firm or certain"
      ],
      "id": "en-nail_down-en-verb-rbINtwy1",
      "links": [
        [
          "firm",
          "firm"
        ],
        [
          "certain",
          "certain"
        ]
      ],
      "raw_glosses": [
        "(idiomatic, transitive) to make something (e.g. a decision or plan) firm or certain"
      ],
      "tags": [
        "idiomatic",
        "transitive"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "En-au-nail down.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/c/c0/En-au-nail_down.ogg/En-au-nail_down.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/c/c0/En-au-nail_down.ogg",
      "tags": [
        "Australia"
      ],
      "text": "Audio (AU)"
    }
  ],
  "word": "nail down"
}

{
  "categories": [
    "English entries with incorrect language header",
    "English lemmas",
    "English multiword terms",
    "English phrasal verbs",
    "English phrasal verbs with particle (down)",
    "English terms with audio links",
    "English verbs",
    "en:Construction"
  ],
  "forms": [
    {
      "form": "nails down",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "nailing down",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "nailed down",
      "tags": [
        "participle",
        "past"
      ]
    },
    {
      "form": "nailed down",
      "tags": [
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "*"
      },
      "expansion": "nail down (third-person singular simple present nails down, present participle nailing down, simple past and past participle nailed down)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "related": [
    {
      "word": "copperfasten"
    },
    {
      "word": "pin down"
    }
  ],
  "senses": [
    {
      "categories": [
        "English transitive verbs"
      ],
      "examples": [
        {
          "text": "Nail down the shelf, then paint it."
        }
      ],
      "glosses": [
        "to attach with nails"
      ],
      "links": [
        [
          "nail",
          "nail"
        ]
      ],
      "raw_glosses": [
        "(transitive) to attach with nails"
      ],
      "tags": [
        "transitive"
      ]
    },
    {
      "categories": [
        "English idioms",
        "English transitive verbs"
      ],
      "examples": [
        {
          "text": "They haven't nailed down their vacation plans yet."
        }
      ],
      "glosses": [
        "to make something (e.g. a decision or plan) firm or certain"
      ],
      "links": [
        [
          "firm",
          "firm"
        ],
        [
          "certain",
          "certain"
        ]
      ],
      "raw_glosses": [
        "(idiomatic, transitive) to make something (e.g. a decision or plan) firm or certain"
      ],
      "tags": [
        "idiomatic",
        "transitive"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "En-au-nail down.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/c/c0/En-au-nail_down.ogg/En-au-nail_down.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/c/c0/En-au-nail_down.ogg",
      "tags": [
        "Australia"
      ],
      "text": "Audio (AU)"
    }
  ],
  "word": "nail down"
}