"de fer" meaning in French

{
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      "args": {
        "inv": "1"
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      "expansion": "de fer (invariable)",
      "name": "fr-adj"
    }
  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "topical",
          "langcode": "fr",
          "name": "Heraldry",
          "orig": "fr:Heraldry",
          "parents": [
            "History",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "_dis": "94 6",
          "kind": "other",
          "name": "French entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
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          "source": "w+disamb"
        }
      ],
      "glosses": [
        "iron, Eisenfarbe (a grey tincture)"
      ],
      "id": "en-de_fer-fr-adj-JLLgQd-F",
      "links": [
        [
          "heraldry",
          "heraldry"
        ],
        [
          "iron",
          "iron"
        ],
        [
          "Eisenfarbe",
          "Eisenfarbe"
        ],
        [
          "grey",
          "grey#English"
        ]
      ],
      "raw_glosses": [
        "(heraldry, rare) iron, Eisenfarbe (a grey tincture)"
      ],
      "related": [
        {
          "_dis1": "100 0",
          "word": "d’acier"
        },
        {
          "_dis1": "100 0",
          "word": "d’airain"
        }
      ],
      "tags": [
        "invariable",
        "rare"
      ],
      "topics": [
        "government",
        "heraldry",
        "hobbies",
        "lifestyle",
        "monarchy",
        "nobility",
        "politics"
      ]
    },
    {
      "categories": [],
      "examples": [
        {
          "english": "to be in excellent health, to have a cast-iron constitution",
          "text": "avoir une santé de fer",
          "type": "example"
        },
        {
          "english": "to have a will of iron, an unbending will, an iron determination",
          "text": "avoir une volonté de fer",
          "type": "example"
        }
      ],
      "glosses": [
        "strong, resilient, iron"
      ],
      "id": "en-de_fer-fr-adj-6e5A-ZZb",
      "links": [
        [
          "strong",
          "strong"
        ],
        [
          "resilient",
          "resilient"
        ],
        [
          "iron",
          "iron#English:_tough"
        ]
      ],
      "raw_glosses": [
        "(figuratively) strong, resilient, iron"
      ],
      "tags": [
        "figuratively",
        "invariable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/də fɛʁ/"
    },
    {
      "audio": "LL-Q150 (fra)-LoquaxFR-de fer.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/8/8f/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/8/8f/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav.ogg",
      "text": "Audio"
    }
  ],
  "word": "de fer"
}

{
  "categories": [
    "French adjectives",
    "French entries with incorrect language header",
    "French lemmas",
    "French multiword terms",
    "French terms with IPA pronunciation",
    "French terms with audio links"
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  "head_templates": [
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      "args": {
        "inv": "1"
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      "expansion": "de fer (invariable)",
      "name": "fr-adj"
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  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "adj",
  "related": [
    {
      "word": "d’acier"
    },
    {
      "word": "d’airain"
    }
  ],
  "senses": [
    {
      "categories": [
        "French terms with rare senses",
        "fr:Heraldry"
      ],
      "glosses": [
        "iron, Eisenfarbe (a grey tincture)"
      ],
      "links": [
        [
          "heraldry",
          "heraldry"
        ],
        [
          "iron",
          "iron"
        ],
        [
          "Eisenfarbe",
          "Eisenfarbe"
        ],
        [
          "grey",
          "grey#English"
        ]
      ],
      "raw_glosses": [
        "(heraldry, rare) iron, Eisenfarbe (a grey tincture)"
      ],
      "tags": [
        "invariable",
        "rare"
      ],
      "topics": [
        "government",
        "heraldry",
        "hobbies",
        "lifestyle",
        "monarchy",
        "nobility",
        "politics"
      ]
    },
    {
      "categories": [
        "French terms with usage examples"
      ],
      "examples": [
        {
          "english": "to be in excellent health, to have a cast-iron constitution",
          "text": "avoir une santé de fer",
          "type": "example"
        },
        {
          "english": "to have a will of iron, an unbending will, an iron determination",
          "text": "avoir une volonté de fer",
          "type": "example"
        }
      ],
      "glosses": [
        "strong, resilient, iron"
      ],
      "links": [
        [
          "strong",
          "strong"
        ],
        [
          "resilient",
          "resilient"
        ],
        [
          "iron",
          "iron#English:_tough"
        ]
      ],
      "raw_glosses": [
        "(figuratively) strong, resilient, iron"
      ],
      "tags": [
        "figuratively",
        "invariable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/də fɛʁ/"
    },
    {
      "audio": "LL-Q150 (fra)-LoquaxFR-de fer.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/8/8f/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/8/8f/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav/LL-Q150_%28fra%29-LoquaxFR-de_fer.wav.ogg",
      "text": "Audio"
    }
  ],
  "word": "de fer"
}