"four-velocity" meaning in English

{
  "forms": [
    {
      "form": "four-velocities",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "four-velocity (plural four-velocities)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Mandarin terms with redundant transliterations",
          "parents": [
            "Terms with redundant transliterations",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Physics",
          "orig": "en:Physics",
          "parents": [
            "Sciences",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A generalization of velocity in four-dimensional spacetime"
      ],
      "id": "en-four-velocity-en-noun-qBeNAmLl",
      "links": [
        [
          "physics",
          "physics"
        ],
        [
          "four-dimensional",
          "four-dimensional"
        ],
        [
          "spacetime",
          "spacetime"
        ]
      ],
      "raw_glosses": [
        "(physics) A generalization of velocity in four-dimensional spacetime"
      ],
      "topics": [
        "natural-sciences",
        "physical-sciences",
        "physics"
      ],
      "translations": [
        {
          "code": "cmn",
          "lang": "Chinese Mandarin",
          "sense": "generalization of velocity",
          "word": "四維速度"
        },
        {
          "code": "cmn",
          "lang": "Chinese Mandarin",
          "roman": "sìwéi sùdù",
          "sense": "generalization of velocity",
          "word": "四维速度"
        },
        {
          "code": "it",
          "lang": "Italian",
          "sense": "generalization of velocity",
          "tags": [
            "feminine"
          ],
          "word": "quadrivelocità"
        }
      ],
      "wikipedia": [
        "four-velocity"
      ]
    }
  ],
  "word": "four-velocity"
}

{
  "forms": [
    {
      "form": "four-velocities",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "four-velocity (plural four-velocities)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Mandarin terms with redundant transliterations",
        "en:Physics"
      ],
      "glosses": [
        "A generalization of velocity in four-dimensional spacetime"
      ],
      "links": [
        [
          "physics",
          "physics"
        ],
        [
          "four-dimensional",
          "four-dimensional"
        ],
        [
          "spacetime",
          "spacetime"
        ]
      ],
      "raw_glosses": [
        "(physics) A generalization of velocity in four-dimensional spacetime"
      ],
      "topics": [
        "natural-sciences",
        "physical-sciences",
        "physics"
      ],
      "wikipedia": [
        "four-velocity"
      ]
    }
  ],
  "translations": [
    {
      "code": "cmn",
      "lang": "Chinese Mandarin",
      "sense": "generalization of velocity",
      "word": "四維速度"
    },
    {
      "code": "cmn",
      "lang": "Chinese Mandarin",
      "roman": "sìwéi sùdù",
      "sense": "generalization of velocity",
      "word": "四维速度"
    },
    {
      "code": "it",
      "lang": "Italian",
      "sense": "generalization of velocity",
      "tags": [
        "feminine"
      ],
      "word": "quadrivelocità"
    }
  ],
  "word": "four-velocity"
}