1.
recoil, reaction, backlash
A force or movement that occurs in response to a prior action, often in the opposite direction. Can be physical or metaphorical.
無理した反動で体調を崩した。
I got sick as a backlash from overworking.
ダイエットの反動で食べ過ぎた。
I overate as a rebound from dieting.
厳しい規制の反動で、自由化を求める声が高まった。
As a backlash against strict regulations, calls for liberalization grew louder.
2.
reactionary (political)
In a political context, opposition to progress or reform, favoring a return to a previous state.
反動勢力が台頭した。
Reactionary forces rose to prominence.
反動的な思想に批判が集まった。
Reactionary ideology drew criticism.
改革に対する反動として保守派が勢力を伸ばした。
As a reaction against reform, the conservatives expanded their influence.
反動 describes a reaction or backlash that occurs in the opposite direction of a prior action. In everyday Japanese, it most commonly refers to a rebound effect — overdoing something after a period of restraint.
COMMON PATTERNS:
- 〜の反動で: as a rebound/backlash from ~
- 反動が来る: to experience a rebound/backlash
- 反動が大きい: the backlash is severe
COMMON COLLOCATIONS:
- ダイエットの反動: rebound from dieting
- 無理した反動: backlash from overexertion
- 反動的: reactionary (na-adjective)
- 反動勢力: reactionary forces (political)
USAGE:
In everyday conversation, the rebound/backlash sense (sense 1) is far more common. The political sense (reactionary) appears mainly in news and academic writing.