"trunk piston" meaning in English

{
  "forms": [
    {
      "form": "trunk pistons",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "trunk piston (plural trunk pistons)",
      "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"
        }
      ],
      "glosses": [
        "In a single-acting engine, an elongated hollow piston, open at the end, in which the end of the connecting rod is pivoted. The piston rod, crosshead and stuffing box are thus dispensed with."
      ],
      "id": "en-trunk_piston-en-noun-xQKXe-iW"
    }
  ],
  "word": "trunk piston"
}

{
  "forms": [
    {
      "form": "trunk pistons",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "trunk piston (plural trunk pistons)",
      "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"
      ],
      "glosses": [
        "In a single-acting engine, an elongated hollow piston, open at the end, in which the end of the connecting rod is pivoted. The piston rod, crosshead and stuffing box are thus dispensed with."
      ]
    }
  ],
  "word": "trunk piston"
}