"vernier engine" meaning in Anglais

{
  "categories": [
    {
      "kind": "other",
      "name": "Locutions nominales en anglais",
      "parents": [],
      "source": "w"
    },
    {
      "kind": "other",
      "name": "Anglais",
      "orig": "anglais",
      "parents": [],
      "source": "w"
    }
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "Lexique en anglais de la propulsion spatiale",
          "parents": [],
          "source": "w"
        }
      ],
      "glosses": [
        "Moteur vernier."
      ],
      "id": "fr-vernier_engine-en-noun-gDsSboVn",
      "raw_tags": [
        "Propulsion spatiale"
      ]
    }
  ],
  "word": "vernier engine"
}

{
  "categories": [
    "Locutions nominales en anglais",
    "anglais"
  ],
  "lang": "Anglais",
  "lang_code": "en",
  "pos": "noun",
  "pos_title": "Locution nominale",
  "senses": [
    {
      "categories": [
        "Lexique en anglais de la propulsion spatiale"
      ],
      "glosses": [
        "Moteur vernier."
      ],
      "raw_tags": [
        "Propulsion spatiale"
      ]
    }
  ],
  "word": "vernier engine"
}