"sīdǐxià" meaning in Mandarin

{
  "forms": [
    {
      "form": "ㄙ ㄉㄧˇ ㄒㄧㄚˋ",
      "tags": [
        "bopomofo"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "sīdǐxià (Zhuyin ㄙ ㄉㄧˇ ㄒㄧㄚˋ)",
      "name": "cmn-pinyin"
    }
  ],
  "lang": "Mandarin",
  "lang_code": "cmn",
  "pos": "romanization",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Hanyu Pinyin",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Mandarin entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Mandarin terms with redundant script codes",
          "parents": [
            "Terms with redundant script codes",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Hanyu Pinyin reading of 私底下"
      ],
      "id": "en-sīdǐxià-cmn-romanization-zaajyAhN",
      "links": [
        [
          "Hanyu Pinyin",
          "Hanyu Pinyin"
        ],
        [
          "私底下",
          "私底下#Chinese"
        ]
      ]
    }
  ],
  "word": "sīdǐxià"
}

{
  "forms": [
    {
      "form": "ㄙ ㄉㄧˇ ㄒㄧㄚˋ",
      "tags": [
        "bopomofo"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "sīdǐxià (Zhuyin ㄙ ㄉㄧˇ ㄒㄧㄚˋ)",
      "name": "cmn-pinyin"
    }
  ],
  "lang": "Mandarin",
  "lang_code": "cmn",
  "pos": "romanization",
  "senses": [
    {
      "categories": [
        "Hanyu Pinyin",
        "Mandarin entries with incorrect language header",
        "Mandarin non-lemma forms",
        "Mandarin terms with redundant script codes"
      ],
      "glosses": [
        "Hanyu Pinyin reading of 私底下"
      ],
      "links": [
        [
          "Hanyu Pinyin",
          "Hanyu Pinyin"
        ],
        [
          "私底下",
          "私底下#Chinese"
        ]
      ]
    }
  ],
  "word": "sīdǐxià"
}