"plain clothes" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "p"
      },
      "expansion": "plain clothes pl (plural only)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
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          "source": "w"
        },
        {
          "kind": "other",
          "name": "English pluralia tantum",
          "parents": [
            "Pluralia tantum",
            "Nouns",
            "Lemmas"
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          "source": "w"
        },
        {
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          "parents": [],
          "source": "w"
        },
        {
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          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Clothing",
          "orig": "en:Clothing",
          "parents": [
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Civilian clothes worn by someone in an occupation or organization for which a uniform might be expected, as the police or clergy."
      ],
      "id": "en-plain_clothes-en-noun-PuChDRMW",
      "links": [
        [
          "Civilian",
          "civilian"
        ],
        [
          "police",
          "police"
        ],
        [
          "clergy",
          "clergy"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "attributive"
          ],
          "word": "plain-clothes"
        }
      ],
      "tags": [
        "plural",
        "plural-only"
      ]
    }
  ],
  "word": "plain clothes"
}

{
  "head_templates": [
    {
      "args": {
        "1": "p"
      },
      "expansion": "plain clothes pl (plural only)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English pluralia tantum",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Clothing"
      ],
      "glosses": [
        "Civilian clothes worn by someone in an occupation or organization for which a uniform might be expected, as the police or clergy."
      ],
      "links": [
        [
          "Civilian",
          "civilian"
        ],
        [
          "police",
          "police"
        ],
        [
          "clergy",
          "clergy"
        ]
      ],
      "tags": [
        "plural",
        "plural-only"
      ]
    }
  ],
  "synonyms": [
    {
      "tags": [
        "attributive"
      ],
      "word": "plain-clothes"
    }
  ],
  "word": "plain clothes"
}

{
  "called_from": "form_description/20250107",
  "msg": "Form tags without form: desc='plural plural-only', tagsets=[('plural', 'plural-only')]",
  "path": [
    "plain clothes"
  ],
  "section": "English",
  "subsection": "noun",
  "title": "plain clothes",
  "trace": ""
}