"su" meaning in Finnish

{
  "head_templates": [
    {
      "args": {
        "1": "fi",
        "2": "noun"
      },
      "expansion": "su",
      "name": "head"
    }
  ],
  "lang": "Finnish",
  "lang_code": "fi",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "Sunday",
          "word": "sunnuntai"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Finnish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Abbreviation of sunnuntai (“Sunday”)."
      ],
      "id": "en-su-fi-noun-t1BZxozu",
      "links": [
        [
          "sunnuntai",
          "sunnuntai#Finnish"
        ]
      ],
      "tags": [
        "abbreviation",
        "alt-of"
      ]
    }
  ],
  "word": "su"
}

{
  "categories": [
    "White Hmong entries with incorrect language header",
    "White Hmong lemmas",
    "White Hmong terms with IPA pronunciation",
    "White Hmong verbs"
  ],
  "head_templates": [
    {
      "args": {
        "1": "fi",
        "2": "noun"
      },
      "expansion": "su",
      "name": "head"
    }
  ],
  "lang": "Finnish",
  "lang_code": "fi",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "extra": "Sunday",
          "word": "sunnuntai"
        }
      ],
      "categories": [
        "Finnish abbreviations",
        "Finnish entries with incorrect language header",
        "Finnish lemmas",
        "Finnish nouns"
      ],
      "glosses": [
        "Abbreviation of sunnuntai (“Sunday”)."
      ],
      "links": [
        [
          "sunnuntai",
          "sunnuntai#Finnish"
        ]
      ],
      "tags": [
        "abbreviation",
        "alt-of"
      ]
    }
  ],
  "word": "su"
}