"feedwater heater" meaning in English

{
  "forms": [
    {
      "form": "feedwater heaters",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "feedwater heater (plural feedwater heaters)",
      "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": "topical",
          "langcode": "en",
          "name": "Rail transportation",
          "orig": "en:Rail transportation",
          "parents": [
            "Transport",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "derived": [
        {
          "word": "closed feedwater heater"
        },
        {
          "word": "open feedwater heater"
        }
      ],
      "glosses": [
        "a device used to preheat water before it enters a boiler. They were at one time also fitted to steam locomotives."
      ],
      "id": "en-feedwater_heater-en-noun-vyy3ahAG",
      "links": [
        [
          "preheat",
          "preheat"
        ],
        [
          "boiler",
          "boiler"
        ],
        [
          "steam locomotive",
          "steam locomotive"
        ]
      ]
    }
  ],
  "word": "feedwater heater"
}

{
  "derived": [
    {
      "word": "closed feedwater heater"
    },
    {
      "word": "open feedwater heater"
    }
  ],
  "forms": [
    {
      "form": "feedwater heaters",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "feedwater heater (plural feedwater heaters)",
      "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",
        "en:Rail transportation"
      ],
      "glosses": [
        "a device used to preheat water before it enters a boiler. They were at one time also fitted to steam locomotives."
      ],
      "links": [
        [
          "preheat",
          "preheat"
        ],
        [
          "boiler",
          "boiler"
        ],
        [
          "steam locomotive",
          "steam locomotive"
        ]
      ]
    }
  ],
  "word": "feedwater heater"
}