Learn English – The right word to indicate someone that reacts to something

single-word-requeststerminology

My first question here, let me know if I am missing some details.

Basically, I need to find the right word to represent a specific entity.

How can I call someone who reacts to something? Not necessarily in an impulsive way. Just reacting to something.

At first, I thought something about "reagent" but I discovered it's a technical (chemistry) word.

Best Answer

You could use the word responder, derived from the verb to respond:

to do something as a reaction to something that has happened or been done

source: Merriam-Webster