"sis" meaning in Tok Pisin

{
  "etymology_templates": [
    {
      "args": {
        "1": "tpi",
        "2": "en",
        "3": "cheese"
      },
      "expansion": "English cheese",
      "name": "der"
    }
  ],
  "etymology_text": "From English cheese.",
  "head_templates": [
    {
      "args": {
        "1": "tpi",
        "2": "noun"
      },
      "expansion": "sis",
      "name": "head"
    }
  ],
  "lang": "Tok Pisin",
  "lang_code": "tpi",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Tok Pisin entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "tpi",
          "name": "Cheeses",
          "orig": "tpi:Cheeses",
          "parents": [
            "Dairy products",
            "Foods",
            "Food and drink",
            "Eating",
            "All topics",
            "Human behaviour",
            "Fundamental",
            "Human"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "cheese"
      ],
      "id": "en-sis-tpi-noun-hzrJ~-pN",
      "links": [
        [
          "cheese",
          "cheese"
        ]
      ]
    }
  ],
  "word": "sis"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "tpi",
        "2": "en",
        "3": "cheese"
      },
      "expansion": "English cheese",
      "name": "der"
    }
  ],
  "etymology_text": "From English cheese.",
  "head_templates": [
    {
      "args": {
        "1": "tpi",
        "2": "noun"
      },
      "expansion": "sis",
      "name": "head"
    }
  ],
  "lang": "Tok Pisin",
  "lang_code": "tpi",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Tok Pisin entries with incorrect language header",
        "Tok Pisin lemmas",
        "Tok Pisin nouns",
        "Tok Pisin palindromes",
        "Tok Pisin terms derived from English",
        "tpi:Cheeses"
      ],
      "glosses": [
        "cheese"
      ],
      "links": [
        [
          "cheese",
          "cheese"
        ]
      ]
    }
  ],
  "word": "sis"
}