"úff" meaning in Icelandic

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "interjection"
      },
      "expansion": "úff",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "intj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Icelandic entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "oof! (expresses that something is difficult or painful)"
      ],
      "id": "en-úff-is-intj-xmjifAAb",
      "links": [
        [
          "oof",
          "oof"
        ]
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ufː/"
    },
    {
      "rhymes": "-ufː"
    }
  ],
  "word": "úff"
}

{
  "head_templates": [
    {
      "args": {
        "1": "is",
        "2": "interjection"
      },
      "expansion": "úff",
      "name": "head"
    }
  ],
  "lang": "Icelandic",
  "lang_code": "is",
  "pos": "intj",
  "senses": [
    {
      "categories": [
        "Icelandic 1-syllable words",
        "Icelandic entries with incorrect language header",
        "Icelandic interjections",
        "Icelandic lemmas",
        "Icelandic terms with IPA pronunciation",
        "Rhymes:Icelandic/ufː",
        "Rhymes:Icelandic/ufː/1 syllable"
      ],
      "glosses": [
        "oof! (expresses that something is difficult or painful)"
      ],
      "links": [
        [
          "oof",
          "oof"
        ]
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ufː/"
    },
    {
      "rhymes": "-ufː"
    }
  ],
  "word": "úff"
}