"doubly labeled water" meaning in English

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      "expansion": "doubly labeled water (uncountable)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
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        {
          "kind": "other",
          "langcode": "en",
          "name": "Deuterium",
          "orig": "en:Deuterium",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Isotopes",
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        {
          "kind": "topical",
          "langcode": "en",
          "name": "Oxygen",
          "orig": "en:Oxygen",
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          "kind": "topical",
          "langcode": "en",
          "name": "Physical chemistry",
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        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Water",
          "orig": "en:Water",
          "parents": [
            "Liquids",
            "Matter",
            "Chemistry",
            "Nature",
            "Sciences",
            "All topics",
            "Fundamental"
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        }
      ],
      "examples": [
        {
          "text": "Deuterium oxide-18 (D₂¹⁸O or ²H₂¹⁸O) is one kind of doubly labeled water."
        }
      ],
      "glosses": [
        "Water where both the hydrogen and oxygen atoms have been replaced by less common isotopes."
      ],
      "id": "en-doubly_labeled_water-en-noun-6bQrZI8l",
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        [
          "physical chemistry",
          "physical chemistry"
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        [
          "hydrogen",
          "hydrogen"
        ],
        [
          "oxygen",
          "oxygen"
        ],
        [
          "isotope",
          "isotope"
        ]
      ],
      "raw_glosses": [
        "(physical chemistry, American spelling) Water where both the hydrogen and oxygen atoms have been replaced by less common isotopes."
      ],
      "related": [
        {
          "word": "deuterium"
        },
        {
          "word": "deuterium oxide"
        },
        {
          "word": "heavy water"
        },
        {
          "word": "oxygen-17"
        },
        {
          "word": "oxygen-18"
        },
        {
          "word": "tritiated water"
        }
      ],
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        "US",
        "physical",
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      "topics": [
        "chemistry",
        "natural-sciences",
        "physical-sciences"
      ]
    }
  ],
  "word": "doubly labeled water"
}

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      "expansion": "doubly labeled water (uncountable)",
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  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "deuterium"
    },
    {
      "word": "deuterium oxide"
    },
    {
      "word": "heavy water"
    },
    {
      "word": "oxygen-17"
    },
    {
      "word": "oxygen-18"
    },
    {
      "word": "tritiated water"
    }
  ],
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      "examples": [
        {
          "text": "Deuterium oxide-18 (D₂¹⁸O or ²H₂¹⁸O) is one kind of doubly labeled water."
        }
      ],
      "glosses": [
        "Water where both the hydrogen and oxygen atoms have been replaced by less common isotopes."
      ],
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        [
          "physical chemistry",
          "physical chemistry"
        ],
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          "hydrogen",
          "hydrogen"
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        "(physical chemistry, American spelling) Water where both the hydrogen and oxygen atoms have been replaced by less common isotopes."
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      "topics": [
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  "word": "doubly labeled water"
}