"en connaître un rayon" meaning in French

{
  "etymology_templates": [
    {
      "args": {
        "1": "to know a bookshelf (about it)"
      },
      "expansion": "“to know a bookshelf (about it)”",
      "name": "m-g"
    },
    {
      "args": {
        "1": "to know a bookshelf (about it)"
      },
      "expansion": "Literally, “to know a bookshelf (about it)”",
      "name": "lit"
    }
  ],
  "etymology_text": "Literally, “to know a bookshelf (about it)”.",
  "head_templates": [
    {
      "args": {},
      "expansion": "en connaître un rayon",
      "name": "fr-verb"
    }
  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "French entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "French verbs with placeholder en",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "to know a fair bit about something, to know a thing or two about something, to know one's stuff, to know one's onions"
      ],
      "id": "en-en_connaître_un_rayon-fr-verb-WlAsw~-n",
      "links": [
        [
          "know",
          "know"
        ],
        [
          "a thing or two",
          "a thing or two"
        ],
        [
          "know one's stuff",
          "know one's stuff"
        ],
        [
          "know one's onions",
          "know one's onions"
        ]
      ],
      "raw_glosses": [
        "(informal) to know a fair bit about something, to know a thing or two about something, to know one's stuff, to know one's onions"
      ],
      "synonyms": [
        {
          "word": "s'y connaître"
        }
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ɑ̃ kɔ.nɛ.tʁ‿œ̃ ʁɛ.jɔ̃/"
    },
    {
      "ipa": "/ɑ̃ kɔ.ne.tʁ‿œ̃ ʁe.jɔ̃/"
    },
    {
      "audio": "LL-Q150 (fra)-LoquaxFR-en connaître un rayon.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/0/07/LL-Q150_%28fra%29-LoquaxFR-en_conna%C3%AEtre_un_rayon.wav/LL-Q150_%28fra%29-LoquaxFR-en_conna%C3%AEtre_un_rayon.wav.mp3",
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    }
  ],
  "word": "en connaître un rayon"
}

{
  "etymology_templates": [
    {
      "args": {
        "1": "to know a bookshelf (about it)"
      },
      "expansion": "“to know a bookshelf (about it)”",
      "name": "m-g"
    },
    {
      "args": {
        "1": "to know a bookshelf (about it)"
      },
      "expansion": "Literally, “to know a bookshelf (about it)”",
      "name": "lit"
    }
  ],
  "etymology_text": "Literally, “to know a bookshelf (about it)”.",
  "head_templates": [
    {
      "args": {},
      "expansion": "en connaître un rayon",
      "name": "fr-verb"
    }
  ],
  "lang": "French",
  "lang_code": "fr",
  "pos": "verb",
  "senses": [
    {
      "categories": [
        "French entries with incorrect language header",
        "French informal terms",
        "French lemmas",
        "French multiword terms",
        "French terms with IPA pronunciation",
        "French verbs",
        "French verbs with placeholder en",
        "Pages with 1 entry",
        "Pages with entries"
      ],
      "glosses": [
        "to know a fair bit about something, to know a thing or two about something, to know one's stuff, to know one's onions"
      ],
      "links": [
        [
          "know",
          "know"
        ],
        [
          "a thing or two",
          "a thing or two"
        ],
        [
          "know one's stuff",
          "know one's stuff"
        ],
        [
          "know one's onions",
          "know one's onions"
        ]
      ],
      "raw_glosses": [
        "(informal) to know a fair bit about something, to know a thing or two about something, to know one's stuff, to know one's onions"
      ],
      "synonyms": [
        {
          "word": "s'y connaître"
        }
      ],
      "tags": [
        "informal"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/ɑ̃ kɔ.nɛ.tʁ‿œ̃ ʁɛ.jɔ̃/"
    },
    {
      "ipa": "/ɑ̃ kɔ.ne.tʁ‿œ̃ ʁe.jɔ̃/"
    },
    {
      "audio": "LL-Q150 (fra)-LoquaxFR-en connaître un rayon.wav",
      "mp3_url": "https://upload.wikimedia.org/wikipedia/commons/transcoded/0/07/LL-Q150_%28fra%29-LoquaxFR-en_conna%C3%AEtre_un_rayon.wav/LL-Q150_%28fra%29-LoquaxFR-en_conna%C3%AEtre_un_rayon.wav.mp3",
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    }
  ],
  "word": "en connaître un rayon"
}