"◌̈" meaning in Greek

{
  "lang": "Greek",
  "lang_code": "el",
  "pos": "character",
  "senses": [
    {
      "categories": [
        {
          "kind": "topical",
          "name": "Greek diacritical marks",
          "parents": [
            "Diacritical marks",
            "Letters, symbols, and punctuation",
            "Symbols",
            "Orthography",
            "Writing",
            "Human behaviour",
            "Language",
            "Human",
            "Communication",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Greek entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Greek terms in nonstandard scripts",
          "parents": [
            "Terms in nonstandard scripts",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A diacritical mark of the Greek script, called διαλυτικά in Greek, and found on ί/ΐ/ϋ."
      ],
      "id": "en-◌̈-el-character-H6NT-ymQ",
      "links": [
        [
          "diacritical mark",
          "diacritical mark"
        ],
        [
          "διαλυτικά",
          "διαλυτικά"
        ],
        [
          "ί",
          "ί"
        ],
        [
          "ΐ",
          "ΐ"
        ],
        [
          "ϋ",
          "ϋ"
        ]
      ],
      "tags": [
        "diacritic"
      ]
    }
  ],
  "word": "◌̈"
}

{
  "lang": "Greek",
  "lang_code": "el",
  "pos": "character",
  "senses": [
    {
      "categories": [
        "Greek diacritical marks",
        "Greek entries with incorrect language header",
        "Greek lemmas",
        "Greek terms in nonstandard scripts"
      ],
      "glosses": [
        "A diacritical mark of the Greek script, called διαλυτικά in Greek, and found on ί/ΐ/ϋ."
      ],
      "links": [
        [
          "diacritical mark",
          "diacritical mark"
        ],
        [
          "διαλυτικά",
          "διαλυτικά"
        ],
        [
          "ί",
          "ί"
        ],
        [
          "ΐ",
          "ΐ"
        ],
        [
          "ϋ",
          "ϋ"
        ]
      ],
      "tags": [
        "diacritic"
      ]
    }
  ],
  "word": "◌̈"
}