"accession country" meaning in English

{
  "forms": [
    {
      "form": "accession countries",
      "tags": [
        "plural"
      ]
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  "head_templates": [
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      "args": {},
      "expansion": "accession country (plural accession countries)",
      "name": "en-noun"
    }
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
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      "categories": [
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          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
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          "source": "w"
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      ],
      "glosses": [
        "A country in the process of joining the European Union"
      ],
      "id": "en-accession_country-en-noun-L8xSWk3p",
      "links": [
        [
          "country",
          "country"
        ],
        [
          "European Union",
          "European Union"
        ]
      ],
      "wikipedia": [
        "Enlargement of the European Union"
      ]
    }
  ],
  "word": "accession country"
}

{
  "forms": [
    {
      "form": "accession countries",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "accession country (plural accession countries)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "glosses": [
        "A country in the process of joining the European Union"
      ],
      "links": [
        [
          "country",
          "country"
        ],
        [
          "European Union",
          "European Union"
        ]
      ],
      "wikipedia": [
        "Enlargement of the European Union"
      ]
    }
  ],
  "word": "accession country"
}