"blue jack" meaning in English

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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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      "glosses": [
        "copper sulphate"
      ],
      "id": "en-blue_jack-en-noun-KpL2sSQf",
      "links": [
        [
          "copper sulphate",
          "copper sulphate"
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      "tags": [
        "uncountable"
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    }
  ],
  "word": "blue jack"
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{
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      "expansion": "blue jack (uncountable)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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      "glosses": [
        "copper sulphate"
      ],
      "links": [
        [
          "copper sulphate",
          "copper sulphate"
        ]
      ],
      "tags": [
        "uncountable"
      ]
    }
  ],
  "word": "blue jack"
}