"reaction" meaning in English

{
  "forms": [
    {
      "form": "reaction",
      "tags": [
        "singular"
      ]
    },
    {
      "form": "reactions",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "expansion": "[POS TABLE]",
      "name": "noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [],
      "examples": [
        {
          "text": "When he asked her to lunch, her first reaction was to say no."
        },
        {
          "text": "In part, McKenna sees the move to smaller cars as a natural reaction to rising gasoline prices."
        },
        {
          "text": "Fast reaction times are common in athletes."
        },
        {
          "text": "When oxygen is added, a chemical reaction begins and heat is released."
        },
        {
          "text": "A severe allergic reaction to the drug has killed five Americans."
        }
      ],
      "glosses": [
        "A reaction is an action that happens because of another action."
      ],
      "id": "simple-reaction-en-noun-UzjjOoUt",
      "raw_tags": [
        "countable & uncountable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/riˈækʃən/"
    },
    {
      "sampa": "/ri'{kS@n/"
    },
    {
      "audio": "en-us-reaction.ogg",
      "tags": [
        "US"
      ]
    }
  ],
  "word": "reaction"
}

{
  "forms": [
    {
      "form": "reaction",
      "tags": [
        "singular"
      ]
    },
    {
      "form": "reactions",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "expansion": "[POS TABLE]",
      "name": "noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "Countable nouns",
        "Uncountable nouns"
      ],
      "examples": [
        {
          "text": "When he asked her to lunch, her first reaction was to say no."
        },
        {
          "text": "In part, McKenna sees the move to smaller cars as a natural reaction to rising gasoline prices."
        },
        {
          "text": "Fast reaction times are common in athletes."
        },
        {
          "text": "When oxygen is added, a chemical reaction begins and heat is released."
        },
        {
          "text": "A severe allergic reaction to the drug has killed five Americans."
        }
      ],
      "glosses": [
        "A reaction is an action that happens because of another action."
      ],
      "raw_tags": [
        "countable & uncountable"
      ]
    }
  ],
  "sounds": [
    {
      "ipa": "/riˈækʃən/"
    },
    {
      "sampa": "/ri'{kS@n/"
    },
    {
      "audio": "en-us-reaction.ogg",
      "tags": [
        "US"
      ]
    }
  ],
  "word": "reaction"
}