verb

 

say/do to say, do, or feel something because of something else that has been said or done

He reacted angrily to her comments.

 

bad effect to become ill because something that you have eaten or used on your body has had a bad effect on you

My skin reacts to most perfumes.

 

substances In science, if a substance reacts with another substance, it changes.

Carbon reacts with oxygen to produce carbon dioxide.