"know one's onions" meaning in English

{
  "forms": [
    {
      "form": "knows one's onions",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "knowing one's onions",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "knew one's onions",
      "tags": [
        "past"
      ]
    },
    {
      "form": "known one's onions",
      "tags": [
        "participle",
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "know<,,knew,known> one's onions"
      },
      "expansion": "know one's onions (third-person singular simple present knows one's onions, present participle knowing one's onions, simple past knew one's onions, past participle known one's onions)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "text": "Joe really knows his onions when it comes to cooking.",
          "type": "example"
        },
        {
          "ref": "2007 February 20, Chris Chibnall, Life on Mars, Season 2, Episode 2",
          "text": "Sam Tyler: Well, our first priority is to make sure the thieves don't strike again. It'll be tricky, 'cause these sorts of gangs rarely have just one target on the go. They've usually researched half a dozen possibilities, waiting for the most opportune circumstances on any of them.\nHarry Woolf: He knows his onions, this lad, eh?\nGene Hunt: Oh, he's a right little smart-arse. So, what do you suggest, Buddha?",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Synonym of know one's stuff, to be knowledgeable about a given subject or task."
      ],
      "id": "en-know_one's_onions-en-verb-4XKGqYe0",
      "links": [
        [
          "know one's stuff",
          "know one's stuff#English"
        ],
        [
          "knowledgeable",
          "knowledgeable"
        ],
        [
          "given",
          "given"
        ],
        [
          "subject",
          "subject"
        ],
        [
          "task",
          "task"
        ]
      ],
      "raw_glosses": [
        "(informal) Synonym of know one's stuff, to be knowledgeable about a given subject or task."
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "know one's stuff"
        },
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "to be knowledgeable about a given subject or task"
        }
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "En-au-know one's onions.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/7/7f/En-au-know_one%27s_onions.ogg/En-au-know_one%27s_onions.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/7/7f/En-au-know_one%27s_onions.ogg",
      "tags": [
        "Australia"
      ],
      "text": "Audio (AU)"
    }
  ],
  "word": "know one's onions"
}

{
  "forms": [
    {
      "form": "knows one's onions",
      "tags": [
        "present",
        "singular",
        "third-person"
      ]
    },
    {
      "form": "knowing one's onions",
      "tags": [
        "participle",
        "present"
      ]
    },
    {
      "form": "knew one's onions",
      "tags": [
        "past"
      ]
    },
    {
      "form": "known one's onions",
      "tags": [
        "participle",
        "past"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "know<,,knew,known> one's onions"
      },
      "expansion": "know one's onions (third-person singular simple present knows one's onions, present participle knowing one's onions, simple past knew one's onions, past participle known one's onions)",
      "name": "en-verb"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        "English entries with incorrect language header",
        "English informal terms",
        "English lemmas",
        "English multiword terms",
        "English terms with audio links",
        "English terms with quotations",
        "English terms with usage examples",
        "English verbs",
        "Quotation templates to be cleaned"
      ],
      "examples": [
        {
          "text": "Joe really knows his onions when it comes to cooking.",
          "type": "example"
        },
        {
          "ref": "2007 February 20, Chris Chibnall, Life on Mars, Season 2, Episode 2",
          "text": "Sam Tyler: Well, our first priority is to make sure the thieves don't strike again. It'll be tricky, 'cause these sorts of gangs rarely have just one target on the go. They've usually researched half a dozen possibilities, waiting for the most opportune circumstances on any of them.\nHarry Woolf: He knows his onions, this lad, eh?\nGene Hunt: Oh, he's a right little smart-arse. So, what do you suggest, Buddha?",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Synonym of know one's stuff, to be knowledgeable about a given subject or task."
      ],
      "links": [
        [
          "know one's stuff",
          "know one's stuff#English"
        ],
        [
          "knowledgeable",
          "knowledgeable"
        ],
        [
          "given",
          "given"
        ],
        [
          "subject",
          "subject"
        ],
        [
          "task",
          "task"
        ]
      ],
      "raw_glosses": [
        "(informal) Synonym of know one's stuff, to be knowledgeable about a given subject or task."
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "know one's stuff"
        },
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "to be knowledgeable about a given subject or task"
        }
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "sounds": [
    {
      "audio": "En-au-know one's onions.ogg",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/7/7f/En-au-know_one%27s_onions.ogg/En-au-know_one%27s_onions.ogg.mp3",
      "ogg_url": "https://upload.wikimedia.org/wikipedia/commons/7/7f/En-au-know_one%27s_onions.ogg",
      "tags": [
        "Australia"
      ],
      "text": "Audio (AU)"
    }
  ],
  "word": "know one's onions"
}