"-աւ" meaning in Old Armenian

{
  "etymology_text": "From the stem vowel -ա- (-a-) + -ւ (-w, “instrumental case marker”).",
  "forms": [
    {
      "form": "-aw",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "xcl",
        "2": "suffix",
        "cat2": "inflectional suffixes"
      },
      "expansion": "-աւ • (-aw)",
      "name": "head"
    }
  ],
  "lang": "Old Armenian",
  "lang_code": "xcl",
  "pos": "suffix",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Old Armenian entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "ամաւ ― amaw ― instrumental case of ամ (am)",
          "type": "example"
        }
      ],
      "glosses": [
        "the instrumental case ending of i-a-stem nouns"
      ],
      "id": "en--աւ-xcl-suffix-4PDoxQUq",
      "related": [
        {
          "roman": "-ov",
          "word": "-ով"
        },
        {
          "roman": "-iw",
          "word": "-իւ"
        }
      ],
      "tags": [
        "morpheme"
      ]
    }
  ],
  "word": "-աւ"
}

{
  "etymology_text": "From the stem vowel -ա- (-a-) + -ւ (-w, “instrumental case marker”).",
  "forms": [
    {
      "form": "-aw",
      "tags": [
        "romanization"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "xcl",
        "2": "suffix",
        "cat2": "inflectional suffixes"
      },
      "expansion": "-աւ • (-aw)",
      "name": "head"
    }
  ],
  "lang": "Old Armenian",
  "lang_code": "xcl",
  "pos": "suffix",
  "related": [
    {
      "roman": "-ov",
      "word": "-ով"
    },
    {
      "roman": "-iw",
      "word": "-իւ"
    }
  ],
  "senses": [
    {
      "categories": [
        "Old Armenian entries with incorrect language header",
        "Old Armenian inflectional suffixes",
        "Old Armenian lemmas",
        "Old Armenian suffixes",
        "Old Armenian terms with usage examples"
      ],
      "examples": [
        {
          "text": "ամաւ ― amaw ― instrumental case of ամ (am)",
          "type": "example"
        }
      ],
      "glosses": [
        "the instrumental case ending of i-a-stem nouns"
      ],
      "tags": [
        "morpheme"
      ]
    }
  ],
  "word": "-աւ"
}