"för ovanlighetens skull" meaning in Swedish

{
  "head_templates": [
    {
      "args": {
        "1": "sv",
        "2": "prepositional phrase"
      },
      "expansion": "för ovanlighetens skull",
      "name": "head"
    }
  ],
  "lang": "Swedish",
  "lang_code": "sv",
  "pos": "prep_phrase",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Swedish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "for once"
      ],
      "id": "en-för_ovanlighetens_skull-sv-prep_phrase-mvsMiNGd",
      "links": [
        [
          "for once",
          "for once"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) for once"
      ],
      "synonyms": [
        {
          "word": "för en gångs skull"
        },
        {
          "word": "för ovanlighets skull"
        }
      ],
      "tags": [
        "idiomatic"
      ]
    }
  ],
  "word": "för ovanlighetens skull"
}

{
  "head_templates": [
    {
      "args": {
        "1": "sv",
        "2": "prepositional phrase"
      },
      "expansion": "för ovanlighetens skull",
      "name": "head"
    }
  ],
  "lang": "Swedish",
  "lang_code": "sv",
  "pos": "prep_phrase",
  "senses": [
    {
      "categories": [
        "Swedish entries with incorrect language header",
        "Swedish idioms",
        "Swedish lemmas",
        "Swedish multiword terms",
        "Swedish prepositional phrases"
      ],
      "glosses": [
        "for once"
      ],
      "links": [
        [
          "for once",
          "for once"
        ]
      ],
      "raw_glosses": [
        "(idiomatic) for once"
      ],
      "synonyms": [
        {
          "word": "för en gångs skull"
        }
      ],
      "tags": [
        "idiomatic"
      ]
    }
  ],
  "synonyms": [
    {
      "word": "för ovanlighets skull"
    }
  ],
  "word": "för ovanlighetens skull"
}