reaction
/riˈækʃn/ (bre, ipa) · /riˈækʃn/ (ame, ipa) · /rē-ˈak-shən/ (ame, mw)
reaction — noun
- reactionsingular
- reactionsplural
1. your way of behaving, feeling, or acting that follows directly from an event or
your way of behaving, feeling, or acting that follows directly from an event or situation — for example, feeling shock after hearing bad news, or clapping when a performance finishes.
Tamar's immediate reaction to the job offer was one of surprise and delight.
immediate reaction + to + noun phrase
The city council's reaction to the housing shortage was to approve new building permits.
reaction + to + noun + verb pattern
Hao had a strong emotional reaction when he heard about the company merger.
There was a mixed reaction from the audience when the singer changed the lyrics.
In reaction to the complaints, the restaurant updated its menu with healthier options.
- indifference
lack of any reaction or emotional response
文法句型
reaction + to + noun/pronoun/gerund
in reaction + to + noun
as a reaction + to + noun
there + be + a reaction + to + noun
用法筆記
Often followed by 'to' to indicate the cause. The verb pattern varies: a reaction can be a feeling, a word, or an action.
常見錯誤
2. a physical change in the body that shows you have a negative sensitivity to a su
a physical change in the body that shows you have a negative sensitivity to a substance such as food, medicine, or pollen — examples include rashes, swelling, breathing difficulty, or an itchy feeling after eating something you are allergic to.
Marta had a severe allergic reaction to the shellfish and needed urgent medical attention.
allergic reaction + to + substance — medical collocation
Ravindra developed a red, itchy skin reaction three days after starting the penicillin treatment.
Ife developed a bad reaction to the medication and had to stop using it immediately.
The doctor asked about any previous reaction to anaesthesia before the operation began.
- allergy
the long-term condition, not the individual event; 'reaction' is a single episode
- response
neutral; 'reaction' in this sense implies negative sensitivity
- side effect
broader — includes any unintended effect, not just allergic ones
文法句型
reaction + to + noun (substance/formula)
have + a + reaction + to + noun
experience + a + reaction
用法筆記
Medical context. 'Reaction' can be mild (slight rash) or severe (anaphylaxis). 'Adverse reaction' is a formal medical term for any unwanted drug effect, not just allergy.
常見錯誤
3. the speed with which someone can act or respond when something unexpected happen
the speed with which someone can act or respond when something unexpected happens — used especially about physical reflexes, such as a driver braking to avoid a crash or a goalkeeper saving a shot.
The driver's quick reaction prevented a serious accident on the icy highway.
quick reaction — adjective + reaction describing speed
A good goalkeeper needs excellent reactions to stop a fast-moving penalty kick.
Yuki noticed that her reaction time behind the wheel was slower than it had been ten years ago.
Dewi's fast reaction saved the child from stepping into the busy street.
文法句型
reaction + time(s)
have + adjective + reactions
quick/fast/good reactions
用法筆記
In this sense 'reactions' (plural) is common in British English ('She has good reactions'). 'Reaction time' (singular) is the standard term in sports science and psychology.
常見錯誤
4. [chemistry] a change where substances interact and turn into new materials — for
[chemistry] a change where substances interact and turn into new materials — for example, iron rusting when it meets oxygen and water, or an acid and a base combining to create salt and water.
The students observed a chemical reaction when they mixed vinegar with baking soda.
chemical reaction — scientific collocation
Iron powder meeting oxygen in a hand warmer pack triggers a reaction that releases enough heat to warm your palms.
released during + reaction — prepositional common pattern
The enzyme amylase speeds up the chemical reaction that breaks down starch into sugar during chewing.
The reaction between the two liquids produced a bright yellow compound.
- chemical process
broader than a single reaction; a process may involve multiple reactions
- transformation
general change, not limited to chemistry
文法句型
chemical + reaction
set off / trigger + a + reaction
reaction + between + noun + and + noun
用法筆記
General term for all chemical transformations. 'Chain reaction' describes a sequence where each step triggers the next, common in nuclear physics. 'Nuclear reaction' is a specific type involving atomic nuclei.
常見錯誤
5. a way of behaving, thinking, or creating that is deliberately the opposite of a
a way of behaving, thinking, or creating that is deliberately the opposite of a previous style, idea, or norm — for example, young people adopting a fashion style that rebels against older generations' tastes.
The teenager's taste in music was a reaction against his parents' classical preferences.
reaction against — followed by 'against'
Filmmaker Chidi adopted a raw, hand-held camera style as a reaction to glossy Hollywood blockbusters.
as a reaction to — prepositional phrase
Designer Mira's Autumn collection felt like a deliberate reaction against last season's neon-bright colours.
Mert's minimalist home was a reaction against the crowded decoration style he grew up with.
- acceptance
embracing rather than opposing the existing norm
文法句型
reaction + against + noun/gerund
as a reaction + to + noun
用法筆記
Frequently followed by 'against' (direct opposition) or 'to' (general response context). This sense carries a deliberate, sometimes ideological tone of rejection.
常見錯誤
6. the position that opposes reform and tries to keep society and politics from cha
the position that opposes reform and tries to keep society and politics from changing — for example, organisations that fight against new laws about equal rights or environmental standards.
The election result was seen as a reaction against the government's education reforms.
reaction against — followed by 'against' in political context
The governor's new tax on farmers triggered a reaction from growers who blocked the highway with their tractors.
triggered a reaction from + [group] who [concrete action]
Historian Adina views the back-to-the-land movement as a reaction to the rapid social changes of the 1960s.
The Rural Heritage Association was called a force of reaction that blocked every new environmental policy proposal.
- conservatism
broader; includes moderate resistance to change; 'reaction' implies stronger opposition and desire to reverse
- traditionalism
focuses on preserving customs rather than opposing change actively
- progressivism
belief in active social or political reform and change
- radicalism
belief in fundamental, rapid change
文法句型
reaction + against + noun
forces of + reaction
用法筆記
This sense is always uncountable ('reaction', not 'a reaction' or 'reactions'). The related noun 'reactionary' describes a person who holds such beliefs. Often carries a negative connotation.
常見錯誤
7. [physics] a force of equal size that pushes backward when one thing pushes again
[physics] a force of equal size that pushes backward when one thing pushes against another — described in Newton's third law, for instance the upward push a rocket gets when it forces hot gas downward.
When Felipe pushes against the wall during a standing vertical jump, the wall's reaction force propels his body upward.
equal and opposite reaction — Newton's third law formula
A jet engine's thrust produces a reaction force that pushes the plane forward.
reaction force — physics collocation
Vinícius learned in physics class that a reaction force always opposes the original action.
Jumping off a small boat creates a reaction that pushes the boat backward.
文法句型
reaction + force
equal and opposite + reaction
action and + reaction
用法筆記
Often paired with 'action' as a fixed pair ('action and reaction'). In physics problems, 'reaction force' refers specifically to the force exerted by a surface against an object resting on it (normal reaction).