Did you know?

Click any word in a definition or example to find the entry for that word

reaction - definition and synonyms

What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.

Thesaurus diagram

The thesaurus of synonyms and related words is fully integrated into the dictionary. Click on the thesaurus category heading under the button in an entry to see the synonyms and related words for that meaning.

noun     reaction pronunciation in American English
Word Forms
  1. 1
    [countable] the way that you feel or behave as a result of something that happens

    My mother’s initial reaction was quite unexpected.

    My parents were pretty surprised at my reaction.

    reaction from/of someone:

    The reaction from the local community was very negative.

    someone’s reaction is to do something:

    Their reaction to the report was to ban trade with those countries.

    mixed reaction (=one in which people reacted differently):

    The Fed chairman’s plan received a mixed reaction on Wall Street last night.

    1. a.
      [usually singular] a sudden feeling of being tired, upset, etc., for example after an unpleasant or exciting experience

      The reaction of any individual trauma victim is difficult to predict.

      reaction to:

      Shock is a natural reaction to such bad news.

    See also knee-jerk
  2. 2
    [countable] a bad effect on your body caused by food, medicine, or another substance
    reaction to:

    Some people’s skin has an allergic reaction to certain types of fabric.

    have/suffer a reaction:

    He suffered a violent reaction to the medicine.

  3. 4
    [singular] an attitude of wanting to do things in a different way from the way that they were done in the past
    reaction against:

    The reaction against traditional styles continued for another 50 years.

  4. 5
    [countable] chemistry a process in which a chemical change happens

    Temperature can affect the rate of a chemical reaction.

    reaction between:

    We are studying reactions between a number of metals and acids.

    1. a.
      [countable/uncountable] physics a physical force that is caused by an opposite physical force, usually producing a form of energy

      a nuclear reaction

      Newton teaches that action and reaction are equal and opposite.

    See also chain reaction
  • Facebook
  • Twitter


a lifestyle focussing on simple pleasures such as comfort and cosiness in the home, and spending time with friends and family

BuzzWord Article

Open Dictionary


a form of location that involves the underwater detonation of a bomb which causes sound waves that are picked up by ships

add a word


A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

global English and language change from our blog
Macmillan learn live love play