"one's back is up" meaning in English

{
  "etymology_text": "From the way a cat, when angry, raises or arches its back.",
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  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
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          "ref": "1835, William Hayley, The Life and Letters of William Cowper:",
          "text": "My back is up, and I cannot hear the thought of wooing him any farther, nor would do it, though he were as pig a gentleman (look you) as Lucifer himself.",
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          "ref": "2011, Jeannie Watt, The Baby Truce, →ISBN, page 84:",
          "text": "And I want you to be nice to Patty. For some reason her back is up.",
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          "ref": "2014, Kristin Butcher, Cabin Girl, →ISBN:",
          "text": "Now my back is up. “Yes, the witch,” I hiss.",
          "type": "quote"
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      ],
      "glosses": [
        "One is offended or angry."
      ],
      "id": "en-one's_back_is_up-en-phrase-S2fxqlG9",
      "raw_glosses": [
        "(idiomatic) One is offended or angry."
      ],
      "related": [
        {
          "word": "get one's back up"
        }
      ],
      "tags": [
        "idiomatic"
      ]
    }
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  "word": "one's back is up"
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{
  "etymology_text": "From the way a cat, when angry, raises or arches its back.",
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  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "phrase",
  "related": [
    {
      "word": "get one's back up"
    }
  ],
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          "ref": "1835, William Hayley, The Life and Letters of William Cowper:",
          "text": "My back is up, and I cannot hear the thought of wooing him any farther, nor would do it, though he were as pig a gentleman (look you) as Lucifer himself.",
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          "ref": "2011, Jeannie Watt, The Baby Truce, →ISBN, page 84:",
          "text": "And I want you to be nice to Patty. For some reason her back is up.",
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          "ref": "2014, Kristin Butcher, Cabin Girl, →ISBN:",
          "text": "Now my back is up. “Yes, the witch,” I hiss.",
          "type": "quote"
        }
      ],
      "glosses": [
        "One is offended or angry."
      ],
      "raw_glosses": [
        "(idiomatic) One is offended or angry."
      ],
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        "idiomatic"
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    }
  ],
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