"on one's guard" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "en",
        "2": "prepositional phrase",
        "head": ""
      },
      "expansion": "on one's guard",
      "name": "head"
    },
    {
      "args": {},
      "expansion": "on one's guard",
      "name": "en-prep phrase"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "senses": [
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      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
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          "source": "w"
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      "examples": [
        {
          "text": "Be on your guard against pickpockets in the railway station.",
          "type": "example"
        },
        {
          "ref": "1944 March and April, Chas. S. Lake, “Some C.M.Es. I Have Known: VIII—Sir H. N. Gresley”, in Railway Magazine, page 74",
          "text": "One had to be on one's guard when thus confronted and, in the course of my numerous meetings with him, I had on occasion to exercise all my wits and be prepared at a moment's notice to parry a very awkward question, to which I would much rather have given a considered reply.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "In a watchful state; alert; vigilant."
      ],
      "id": "en-on_one's_guard-en-prep_phrase-b2hrcVRb",
      "links": [
        [
          "watchful",
          "watchful"
        ],
        [
          "alert",
          "alert"
        ],
        [
          "vigilant",
          "vigilant"
        ]
      ],
      "synonyms": [
        {
          "word": "on the alert"
        }
      ],
      "translations": [
        {
          "code": "fi",
          "lang": "Finnish",
          "sense": "to be vigilant",
          "word": "varuillaan"
        },
        {
          "code": "fr",
          "lang": "French",
          "sense": "to be vigilant",
          "word": "sur ses gardes"
        },
        {
          "code": "mi",
          "lang": "Maori",
          "sense": "to be vigilant",
          "word": "tauwhiro"
        },
        {
          "code": "mi",
          "lang": "Maori",
          "sense": "to be vigilant",
          "word": "ohiti"
        },
        {
          "code": "mi",
          "lang": "Maori",
          "sense": "to be vigilant",
          "word": "ohitu"
        },
        {
          "code": "sv",
          "lang": "Swedish",
          "sense": "to be vigilant",
          "word": "vara på sin vakt"
        }
      ]
    }
  ],
  "word": "on one's guard"
}

{
  "head_templates": [
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      "args": {
        "1": "en",
        "2": "prepositional phrase",
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      "expansion": "on one's guard",
      "name": "head"
    },
    {
      "args": {},
      "expansion": "on one's guard",
      "name": "en-prep phrase"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "prep_phrase",
  "senses": [
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      "examples": [
        {
          "text": "Be on your guard against pickpockets in the railway station.",
          "type": "example"
        },
        {
          "ref": "1944 March and April, Chas. S. Lake, “Some C.M.Es. I Have Known: VIII—Sir H. N. Gresley”, in Railway Magazine, page 74",
          "text": "One had to be on one's guard when thus confronted and, in the course of my numerous meetings with him, I had on occasion to exercise all my wits and be prepared at a moment's notice to parry a very awkward question, to which I would much rather have given a considered reply.",
          "type": "quotation"
        }
      ],
      "glosses": [
        "In a watchful state; alert; vigilant."
      ],
      "links": [
        [
          "watchful",
          "watchful"
        ],
        [
          "alert",
          "alert"
        ],
        [
          "vigilant",
          "vigilant"
        ]
      ],
      "synonyms": [
        {
          "word": "on the alert"
        }
      ]
    }
  ],
  "translations": [
    {
      "code": "fi",
      "lang": "Finnish",
      "sense": "to be vigilant",
      "word": "varuillaan"
    },
    {
      "code": "fr",
      "lang": "French",
      "sense": "to be vigilant",
      "word": "sur ses gardes"
    },
    {
      "code": "mi",
      "lang": "Maori",
      "sense": "to be vigilant",
      "word": "tauwhiro"
    },
    {
      "code": "mi",
      "lang": "Maori",
      "sense": "to be vigilant",
      "word": "ohiti"
    },
    {
      "code": "mi",
      "lang": "Maori",
      "sense": "to be vigilant",
      "word": "ohitu"
    },
    {
      "code": "sv",
      "lang": "Swedish",
      "sense": "to be vigilant",
      "word": "vara på sin vakt"
    }
  ],
  "word": "on one's guard"
}