"double U" meaning in English

{
  "forms": [
    {
      "form": "double Us",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "double U (plural double Us)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "double-u"
        }
      ],
      "glosses": [
        "Alternative form of double-u"
      ],
      "id": "en-double_U-en-noun-5BRnLi7L",
      "links": [
        [
          "double-u",
          "double-u#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    },
    {
      "categories": [
        {
          "_dis": "31 69",
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w+disamb"
        }
      ],
      "examples": [
        {
          "ref": "1942, Playing Tricks with Plants, Popular Science, Vol. 140, No. 3 (March), p. 110",
          "text": "In training a tree in the double U […] only the two topmost buds are allowed to grow on the trunk and two arms."
        }
      ],
      "glosses": [
        "something in the shape of two U's (not of a W)"
      ],
      "id": "en-double_U-en-noun--CRufiqv",
      "related": [
        {
          "_dis1": "22 78",
          "english": "something in the shape of three nested U's",
          "word": "triple U"
        }
      ]
    }
  ],
  "word": "double U"
}

{
  "categories": [
    "English countable nouns",
    "English entries with incorrect language header",
    "English lemmas",
    "English multiword terms",
    "English nouns"
  ],
  "forms": [
    {
      "form": "double Us",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "double U (plural double Us)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "english": "something in the shape of three nested U's",
      "word": "triple U"
    }
  ],
  "senses": [
    {
      "alt_of": [
        {
          "word": "double-u"
        }
      ],
      "glosses": [
        "Alternative form of double-u"
      ],
      "links": [
        [
          "double-u",
          "double-u#English"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative"
      ]
    },
    {
      "examples": [
        {
          "ref": "1942, Playing Tricks with Plants, Popular Science, Vol. 140, No. 3 (March), p. 110",
          "text": "In training a tree in the double U […] only the two topmost buds are allowed to grow on the trunk and two arms."
        }
      ],
      "glosses": [
        "something in the shape of two U's (not of a W)"
      ]
    }
  ],
  "word": "double U"
}