"flat joint" meaning in English

{
  "forms": [
    {
      "form": "flat joints",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "flat joint (plural flat joints)",
      "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"
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          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
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          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Gambling",
          "orig": "en:Gambling",
          "parents": [
            "Games",
            "Recreation",
            "Human activity",
            "Human behaviour",
            "Human",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Synonym of flat store (“crooked gambling establishment”)"
      ],
      "id": "en-flat_joint-en-noun-rXmp3JFm",
      "links": [
        [
          "gambling",
          "gambling#Noun"
        ],
        [
          "flat store",
          "flat store#English"
        ]
      ],
      "raw_glosses": [
        "(gambling, slang) Synonym of flat store (“crooked gambling establishment”)"
      ],
      "synonyms": [
        {
          "extra": "crooked gambling establishment",
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "flat store"
        }
      ],
      "tags": [
        "slang"
      ],
      "topics": [
        "gambling",
        "games"
      ]
    }
  ],
  "word": "flat joint"
}

{
  "forms": [
    {
      "form": "flat joints",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "flat joint (plural flat joints)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
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        "English countable nouns",
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        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English slang",
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        "Pages with entries",
        "en:Gambling"
      ],
      "glosses": [
        "Synonym of flat store (“crooked gambling establishment”)"
      ],
      "links": [
        [
          "gambling",
          "gambling#Noun"
        ],
        [
          "flat store",
          "flat store#English"
        ]
      ],
      "raw_glosses": [
        "(gambling, slang) Synonym of flat store (“crooked gambling establishment”)"
      ],
      "synonyms": [
        {
          "extra": "crooked gambling establishment",
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "flat store"
        }
      ],
      "tags": [
        "slang"
      ],
      "topics": [
        "gambling",
        "games"
      ]
    }
  ],
  "word": "flat joint"
}