リアクション

noun

reaction; response

Commonly used for a visible or social response to something someone says or does, often with emphasis on how the response looks or feels.

• 彼かれのリアクションが大おおげさで、みんな笑わらった。

  His reaction was so exaggerated that everyone laughed.

• この投とう稿こうにはたくさんのリアクションがあった。

  There were many responses to this post.

noun

reaction

Physics use for a reaction, especially as a counterpart to an action; in ordinary Japanese, technical terms such as 反作用 or 反力 may be more specific depending on context.

• 物ぶつ理りの文ぶん脈みゃくでは、作さ用ように対たいするリアクションを反はん作さ用ようと呼よぶ。

  In a physics context, the reaction to an action is called a reaction force.