Other forms: reacted, reacts, reacting
To react is to do or feel something in answer to what has just happened. React badly, how did she react, react to the news.
The preposition is to. In chemistry, substances react with each other to form something new: sodium reacts with water. In medicine, to react to a drug or a food is to have an unwanted response. Note reaction, the noun; reactive, meaning responding rather than planning ahead; and reactionary, which is political and means opposed to progress rather than simply quick to respond.
1verbreactTo do or feel something in answer to what happened.
“Nobody knew how he would react and he said nothing at all.”
synonyms: respond
2verbchangeTo change chemically on contact with something.
“The metal reacts with anything acidic.”
Too few real examples of this word to estimate which sense is commonest.
react is a responding.
Also accepted in games: respond
The word is re-, back, plus act — acting back. It entered English in the seventeenth century as a term in the new physics, and the emotional sense is a later borrowing of the mechanical one.
Proto-Indo-European
*h₂eǵ-
Middle English
acte
English
act
English, today
react
Built from
From re + act. redact. act comes from Middle English acte. From Middle English acte, from Old French acte, from Latin ācta (“register of events”), plural of āctum (“decree, law”), from ago (“to do, to act”), ultimately from Proto-Indo-European h₂éǵeti. Compare German Akte (“file”). Partially displaced deed, from Old English dǣd (“act, deed”).
Etymology from Wiktionary, CC BY-SA