"ʼ" meaning in Navajo

{
  "head_templates": [
    {
      "args": {
        "1": "nv",
        "2": "letter",
        "sort": "ʼ"
      },
      "expansion": "ʼ",
      "name": "head"
    }
  ],
  "lang": "Navajo",
  "lang_code": "nv",
  "pos": "character",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "IPA symbols",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Navajo entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Navajo terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "The nineteenth letter of the Navajo alphabet. It is used before or after a vowel to indicate a glottal stop."
      ],
      "id": "en-ʼ-nv-character-5tqa9HM9",
      "related": [
        {
          "word": "saad niyíłtłáádígíí"
        }
      ],
      "tags": [
        "letter"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ʔ/"
    }
  ],
  "word": "ʼ"
}

{
  "head_templates": [
    {
      "args": {
        "1": "nv",
        "2": "letter",
        "sort": "ʼ"
      },
      "expansion": "ʼ",
      "name": "head"
    }
  ],
  "lang": "Navajo",
  "lang_code": "nv",
  "pos": "character",
  "related": [
    {
      "word": "saad niyíłtłáádígíí"
    }
  ],
  "senses": [
    {
      "categories": [
        "IPA symbols",
        "Navajo entries with incorrect language header",
        "Navajo lemmas",
        "Navajo letters",
        "Navajo terms with IPA pronunciation",
        "Navajo terms with non-redundant non-automated sortkeys"
      ],
      "glosses": [
        "The nineteenth letter of the Navajo alphabet. It is used before or after a vowel to indicate a glottal stop."
      ],
      "tags": [
        "letter"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ʔ/"
    }
  ],
  "word": "ʼ"
}