"sii" meaning in Spanish

{
  "etymology_templates": [
    {
      "args": {
        "1": "es",
        "2": "si"
      },
      "expansion": "si",
      "name": "m"
    },
    {
      "args": {
        "1": "es",
        "2": "en",
        "3": "iff",
        "notext": "1"
      },
      "expansion": "English iff",
      "name": "cal"
    }
  ],
  "etymology_text": "Presumably from si and after English iff.",
  "head_templates": [
    {
      "args": {
        "1": "es",
        "2": "conjunction"
      },
      "expansion": "sii",
      "name": "head"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "conj",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Spanish entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "es",
          "name": "Mathematics",
          "orig": "es:Mathematics",
          "parents": [
            "Formal sciences",
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "iff"
      ],
      "id": "en-sii-es-conj-yWKfxCLJ",
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "iff",
          "iff"
        ]
      ],
      "raw_glosses": [
        "(mathematics) iff"
      ],
      "topics": [
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "sii"
}

{
  "categories": [
    "West Makian entries with incorrect language header",
    "West Makian lemmas",
    "West Makian nouns",
    "West Makian terms in nonstandard scripts",
    "West Makian terms with IPA pronunciation",
    "West Makian verbs"
  ],
  "etymology_templates": [
    {
      "args": {
        "1": "es",
        "2": "si"
      },
      "expansion": "si",
      "name": "m"
    },
    {
      "args": {
        "1": "es",
        "2": "en",
        "3": "iff",
        "notext": "1"
      },
      "expansion": "English iff",
      "name": "cal"
    }
  ],
  "etymology_text": "Presumably from si and after English iff.",
  "head_templates": [
    {
      "args": {
        "1": "es",
        "2": "conjunction"
      },
      "expansion": "sii",
      "name": "head"
    }
  ],
  "lang": "Spanish",
  "lang_code": "es",
  "pos": "conj",
  "senses": [
    {
      "categories": [
        "Spanish conjunctions",
        "Spanish entries with incorrect language header",
        "Spanish lemmas",
        "Spanish terms calqued from English",
        "Spanish terms derived from English",
        "es:Mathematics"
      ],
      "glosses": [
        "iff"
      ],
      "links": [
        [
          "mathematics",
          "mathematics"
        ],
        [
          "iff",
          "iff"
        ]
      ],
      "raw_glosses": [
        "(mathematics) iff"
      ],
      "topics": [
        "mathematics",
        "sciences"
      ]
    }
  ],
  "word": "sii"
}