"sy" meaning in Welsh

{
  "head_templates": [
    {
      "args": {},
      "expansion": "sy (not mutable)",
      "name": "cy-verb form"
    }
  ],
  "lang": "Welsh",
  "lang_code": "cy",
  "pos": "verb",
  "senses": [
    {
      "alt_of": [
        {
          "word": "sydd"
        }
      ],
      "categories": [
        {
          "kind": "other",
          "name": "Welsh entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Alternative form of sydd"
      ],
      "id": "en-sy-cy-verb-z6enlSJO",
      "links": [
        [
          "sydd",
          "sydd#Welsh"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "not-mutable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/sɨː/",
      "tags": [
        "North-Wales"
      ]
    },
    {
      "ipa": "/siː/",
      "tags": [
        "South-Wales"
      ]
    },
    {
      "rhymes": "-ɨː"
    }
  ],
  "word": "sy"
}

{
  "categories": [
    "West Frisian entries with incorrect language header",
    "West Frisian lemmas",
    "West Frisian personal pronouns",
    "West Frisian pronouns",
    "West Frisian terms with IPA pronunciation"
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "sy (not mutable)",
      "name": "cy-verb form"
    }
  ],
  "lang": "Welsh",
  "lang_code": "cy",
  "pos": "verb",
  "senses": [
    {
      "alt_of": [
        {
          "word": "sydd"
        }
      ],
      "categories": [
        "Rhymes:Welsh/ɨː",
        "Rhymes:Welsh/ɨː/1 syllable",
        "Welsh entries with incorrect language header",
        "Welsh non-lemma forms",
        "Welsh non-mutable terms",
        "Welsh terms with IPA pronunciation",
        "Welsh verb forms"
      ],
      "glosses": [
        "Alternative form of sydd"
      ],
      "links": [
        [
          "sydd",
          "sydd#Welsh"
        ]
      ],
      "tags": [
        "alt-of",
        "alternative",
        "not-mutable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/sɨː/",
      "tags": [
        "North-Wales"
      ]
    },
    {
      "ipa": "/siː/",
      "tags": [
        "South-Wales"
      ]
    },
    {
      "rhymes": "-ɨː"
    }
  ],
  "word": "sy"
}