reaction
Pluralreactions
- 1What you do, say, or feel because something has happened.
Like jumping when a loud noise surprises you.
Her first reaction was to laugh at the surprise.
The crowd's reaction to the bad news was loud and angry.
UsageSay a reaction to something (not
incorrect: reaction on).Similarresponse
Note
- 2A change in which one or more substances turn into new substances.
Like baking a cake, where wet and dry parts turn into something new.
Mixing vinegar and baking soda starts a reaction that makes bubbles.
The reaction gave off a lot of heat.
UsageSay a reaction between two substances.
Note
- 3A bad or harmful effect on your body caused by a medicine, food or other substance.
She had a reaction to the new medicine and broke out in a rash.
Peanuts can cause a serious reaction in some children.
UsageYou have a reaction to a medicine or food, often an allergic reaction.
Note
- 4Your ability to move fast when something suddenly happens.
The goalie has amazing reactions and stopped every shot.
Older drivers sometimes have slower reactions at night.
UsageYou have quick reactions or slow reactions: it is about how fast you can move.
Similarreflexes
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Less common meanings
- 5A small icon or emoji you add to a message to show how you feel about it.
Like giving a thumbs-up instead of writing a whole reply.
She left a heart reaction on his photo.
The post got hundreds of laughing reactions.
UsageYou leave a reaction on a post or message.
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- 6The push or pull an object gives back, just as strong as the force on it but in the opposite direction.
When you push on a wall, the reaction from the wall pushes back on your hands just as hard.
A swimmer pushes the water backward, and the reaction moves her forward.
Note
- 7Politics that tries to undo recent changes and bring back an older system, or a time when those ideas grow powerful.
Like turning a clock back to an earlier time.
After the revolution came years of reaction, when the old rulers took back control.
The country slipped into reaction once the reforms failed.
UsageOften reaction against changes, or years of reaction.
Similarbacklash
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Practice
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Origin
It comes from Latin 'reāctiō', built from 're-' meaning 'again' and 'agō' meaning 'to act'.
Checked 5 Nov 2026 · 4 facts
- Reaction comes from Latin reāctiō. en.wiktionary.org
- The Latin word ultimately derives from re- and agō. en.wiktionary.org
- Latin re- means 'again'. en.wiktionary.org
- Latin agō means 'to act'. en.wiktionary.org