"-u-" meaning in Swedish

{
  "etymology_templates": [
    {
      "args": {
        "1": "sv",
        "2": "gmq-osw",
        "3": "-u"
      },
      "expansion": "Old Swedish -u",
      "name": "inh"
    }
  ],
  "etymology_text": "In almost all words from Old Swedish -u, -o, from the Old Swedish genitive form of Germanic feminine ōn-stems.\nAlternates with -o- according to Old Swedish rules of syllable weight, where -o was used after heavy syllables and -u after light.",
  "head_templates": [
    {
      "args": {
        "1": "sv",
        "2": "interfix"
      },
      "expansion": "-u-",
      "name": "head"
    }
  ],
  "lang": "Swedish",
  "lang_code": "sv",
  "pos": "interfix",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Swedish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Swedish interfixes",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Genitival interfix used to link elements in some compounds."
      ],
      "id": "en--u--sv-interfix-pp7MiaKc",
      "related": [
        {
          "word": "-o-"
        },
        {
          "word": "-s-"
        },
        {
          "word": "-a-"
        },
        {
          "word": "-e-"
        }
      ],
      "tags": [
        "morpheme"
      ],
      "wikipedia": [
        "syllable weight"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ɵ/"
    }
  ],
  "word": "-u-"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "sv",
        "2": "gmq-osw",
        "3": "-u"
      },
      "expansion": "Old Swedish -u",
      "name": "inh"
    }
  ],
  "etymology_text": "In almost all words from Old Swedish -u, -o, from the Old Swedish genitive form of Germanic feminine ōn-stems.\nAlternates with -o- according to Old Swedish rules of syllable weight, where -o was used after heavy syllables and -u after light.",
  "head_templates": [
    {
      "args": {
        "1": "sv",
        "2": "interfix"
      },
      "expansion": "-u-",
      "name": "head"
    }
  ],
  "lang": "Swedish",
  "lang_code": "sv",
  "pos": "interfix",
  "related": [
    {
      "word": "-o-"
    },
    {
      "word": "-s-"
    },
    {
      "word": "-a-"
    },
    {
      "word": "-e-"
    }
  ],
  "senses": [
    {
      "categories": [
        "Swedish entries with incorrect language header",
        "Swedish interfixes",
        "Swedish lemmas",
        "Swedish terms derived from Old Swedish",
        "Swedish terms inherited from Old Swedish",
        "Swedish terms with IPA pronunciation"
      ],
      "glosses": [
        "Genitival interfix used to link elements in some compounds."
      ],
      "tags": [
        "morpheme"
      ],
      "wikipedia": [
        "syllable weight"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ɵ/"
    }
  ],
  "word": "-u-"
}