"de cajón" meaning in Spanish

{
  "head_templates": [
    {
      "args": {
        "inv": "1"
      },
      "expansion": "de cajón (invariable)",
      "name": "es-adj"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "plain as day"
      ],
      "id": "en-de_cajón-es-adj-cwBxJWur",
      "links": [
        [
          "plain as day",
          "plain as day"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) plain as day"
      ],
      "tags": [
        "idiomatic",
        "invariable"
      ]
    }
  ],
  "word": "de cajón"
}

{
  "head_templates": [
    {
      "args": {
        "inv": "1"
      },
      "expansion": "de cajón (invariable)",
      "name": "es-adj"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "adj",
  "senses": [
    {
      "categories": [
        "Spanish adjectives",
        "Spanish entries with incorrect language header",
        "Spanish idioms",
        "Spanish indeclinable adjectives",
        "Spanish lemmas",
        "Spanish multiword terms"
      ],
      "glosses": [
        "plain as day"
      ],
      "links": [
        [
          "plain as day",
          "plain as day"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) plain as day"
      ],
      "tags": [
        "idiomatic",
        "invariable"
      ]
    }
  ],
  "word": "de cajón"
}