"mad hatter" meaning in English

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  "etymology_text": "The term is attested since at least the 1790s. See mad as a hatter.",
  "forms": [
    {
      "form": "mad hatters",
      "tags": [
        "plural"
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      "expansion": "mad hatter (plural mad hatters)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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        {
          "kind": "topical",
          "langcode": "en",
          "name": "Fairy tale characters",
          "orig": "en:Fairy tale characters",
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          "kind": "topical",
          "langcode": "en",
          "name": "Lewis Carroll",
          "orig": "en:Lewis Carroll",
          "parents": [
            "Authors",
            "British fiction",
            "Fantasy",
            "Individuals",
            "Literature",
            "People",
            "Fiction",
            "Speculative fiction",
            "Culture",
            "Entertainment",
            "Writing",
            "Human",
            "Artistic works",
            "Genres",
            "Society",
            "Human behaviour",
            "Language",
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      "glosses": [
        "A lunatic; a highly eccentric person."
      ],
      "id": "en-mad_hatter-en-noun-Cf8YZxhq",
      "links": [
        [
          "lunatic",
          "lunatic"
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          "eccentric",
          "eccentric"
        ]
      ],
      "related": [
        {
          "word": "March hare"
        }
      ],
      "wikipedia": [
        "mad hatter"
      ]
    }
  ],
  "word": "mad hatter"
}

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        "2": "mad as a hatter"
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      "expansion": "mad as a hatter",
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  ],
  "etymology_text": "The term is attested since at least the 1790s. See mad as a hatter.",
  "forms": [
    {
      "form": "mad hatters",
      "tags": [
        "plural"
      ]
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  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "March hare"
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        "A lunatic; a highly eccentric person."
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        [
          "eccentric",
          "eccentric"
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      ],
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        "mad hatter"
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  "word": "mad hatter"
}