"road metal" meaning in English

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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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        {
          "kind": "topical",
          "langcode": "en",
          "name": "Roads",
          "orig": "en:Roads",
          "parents": [
            "Road transport",
            "Transport",
            "All topics",
            "Fundamental"
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      "glosses": [
        "Hard dark stone crushed into small pieces used in surfacing roads, for ballast in railway tracks, etc.; gravel; blue metal."
      ],
      "id": "en-road_metal-en-noun-LFyKb0YJ",
      "links": [
        [
          "gravel",
          "gravel"
        ],
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          "blue metal",
          "blue metal"
        ]
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      "tags": [
        "uncountable"
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  "word": "road metal"
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  "lang_code": "en",
  "pos": "noun",
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        "en:Roads"
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      "glosses": [
        "Hard dark stone crushed into small pieces used in surfacing roads, for ballast in railway tracks, etc.; gravel; blue metal."
      ],
      "links": [
        [
          "gravel",
          "gravel"
        ],
        [
          "blue metal",
          "blue metal"
        ]
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  "word": "road metal"
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