"caustic alkali" meaning in English

{
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      "form": "caustic alkalis",
      "tags": [
        "plural"
      ]
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  "head_templates": [
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      "expansion": "caustic alkali (countable and uncountable, plural caustic alkalis)",
      "name": "en-noun"
    }
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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          "kind": "other",
          "name": "English entries with incorrect language header",
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        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Potassium",
          "orig": "en:Potassium",
          "parents": [
            "Alkali metals",
            "Chemical elements",
            "Metals",
            "Matter",
            "Metallurgy",
            "Chemistry",
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        {
          "kind": "topical",
          "langcode": "en",
          "name": "Sodium",
          "orig": "en:Sodium",
          "parents": [
            "Alkali metals",
            "Chemical elements",
            "Metals",
            "Matter",
            "Metallurgy",
            "Chemistry",
            "Nature",
            "Technology",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "The hydrate of potassium (called caustic potash) or sodium (caustic soda)."
      ],
      "id": "en-caustic_alkali-en-noun-ubqazU-t",
      "links": [
        [
          "inorganic chemistry",
          "inorganic chemistry"
        ],
        [
          "hydrate",
          "hydrate"
        ],
        [
          "potassium",
          "potassium"
        ],
        [
          "caustic potash",
          "caustic potash#English"
        ],
        [
          "sodium",
          "sodium"
        ],
        [
          "caustic soda",
          "caustic soda#English"
        ]
      ],
      "raw_glosses": [
        "(inorganic chemistry, dated) The hydrate of potassium (called caustic potash) or sodium (caustic soda)."
      ],
      "tags": [
        "countable",
        "dated",
        "uncountable"
      ],
      "topics": [
        "chemistry",
        "inorganic-chemistry",
        "natural-sciences",
        "physical-sciences"
      ]
    }
  ],
  "word": "caustic alkali"
}

{
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      "form": "caustic alkalis",
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  "lang_code": "en",
  "pos": "noun",
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        "en:Inorganic compounds",
        "en:Potassium",
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      "glosses": [
        "The hydrate of potassium (called caustic potash) or sodium (caustic soda)."
      ],
      "links": [
        [
          "inorganic chemistry",
          "inorganic chemistry"
        ],
        [
          "hydrate",
          "hydrate"
        ],
        [
          "potassium",
          "potassium"
        ],
        [
          "caustic potash",
          "caustic potash#English"
        ],
        [
          "sodium",
          "sodium"
        ],
        [
          "caustic soda",
          "caustic soda#English"
        ]
      ],
      "raw_glosses": [
        "(inorganic chemistry, dated) The hydrate of potassium (called caustic potash) or sodium (caustic soda)."
      ],
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        "countable",
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        "uncountable"
      ],
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    }
  ],
  "word": "caustic alkali"
}