"RTR" meaning in English

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      "expansion": "RTR (uncountable)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "retracted tongue root"
        }
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      ],
      "glosses": [
        "Initialism of retracted tongue root."
      ],
      "id": "en-RTR-en-noun-kZjIxx1j",
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      "raw_glosses": [
        "(phonetics) Initialism of retracted tongue root."
      ],
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      "topics": [
        "human-sciences",
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  ],
  "word": "RTR"
}

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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "alt_of": [
        {
          "word": "retracted tongue root"
        }
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        "English entries with incorrect language header",
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        "English nouns",
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        "en:Phonetics"
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      "glosses": [
        "Initialism of retracted tongue root."
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      "raw_glosses": [
        "(phonetics) Initialism of retracted tongue root."
      ],
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      "topics": [
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        "phonology",
        "sciences"
      ]
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  ],
  "word": "RTR"
}