react

Formsreacts, reacting, reacted

Pluralreacts

1. 1
   verbintransitive

   To act in response to something that happens or is said.

   People react very differently to stress and pressure.

   He reacted angrily to the criticism in the meeting.

   Similarrespond

   Note

   The everyday sense, and the plainest reading of the word's parts: re- plus act, acting back in answer. Redact is its piecewise doublet, built from the same two pieces by a different route. In use, the thing responded to comes in with to. Compare How did she react to the news? with How did she take the news?: take makes the news its object, while react needs the preposition.

2. 2
   verbintransitive

   Of chemical substances, to act upon one another and produce a chemical change.

   Hydrogen and oxygen react to form water.

   Sodium reacts violently when dropped into water.

   Similarcombine

   Note

   In chemistry the word names a real change, not mere contact: bonds break and form, and the products differ in composition or structure from the starting materials. The partner substance takes with (sodium reacts with water), and the result takes to form (hydrogen and oxygen react to form water). The substances themselves are the subject. When a person makes it happen, the verb shifts to its causative partner.

3. 3
   verbintransitive

   To post an emoji or icon on a message to show how one feels about it.

   Thousands of users reacted to the announcement within minutes.

   Friends often react to my posts with laughing faces.

   Similarrespond

   Note

   Social platforms gave the old verb a new, literal job: clicking an icon under a message. The construction follows the everyday "respond" sense, so you react to a post, and the icon itself comes in with with, as in reacting with a heart. Context does the disambiguating. On a feed, someone who reacted may never have typed a word.

4. 4
   verbtransitive

   To cause one chemical substance to undergo a chemical change with another.

   Researchers react hydrogen with nitrogen to produce ammonia.

   The technician reacted the sample with a reagent to test for starch.

   Note

   In this sense the chemist becomes the subject. One reacts A with B: the substance worked on is the direct object, and the second reagent is introduced by with. It is the language of laboratories and methods sections. It describes deliberately bringing substances together under conditions that drive a reaction, whereas the intransitive chemical sense simply reports what substances do to each other.

5. 5
   verbintransitive

   To exert an opposing force in response to the action of another body.

   The ground reacts against your feet with every step you take.

   Solid surfaces react to applied loads with an equal and opposite force.

   Note

   Physics uses the word for the push back that every push receives. In the older phrasing, every body reacts on the body that impels it. It is the reaction of Newton's third law, equal in size and opposite in direction to the applied force. Note the prepositions on and against: they frame the reaction as a force exerted on another body, not as a response to an event.

6. 6
   nouncountable

   An emoji added to a social media post to express how one feels about it.

   The post collected thousands of reacts overnight.

   He dropped a heart react under her photo.

   Similarreaction

   Note

   Internet speech turned the verb into a countable noun for the icon itself, plural reacts. More formal writing would say reaction. The noun is at home in captions and comments. Sad reacts only asks readers to answer a post with the sad face and nothing else. Outside social media it reads as slangy, so reaction is the safer choice in prose.

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