Yes, reaction is a Scrabble word!

Noun

1. (chemistry) a process in which one or more substances are changed into others

2. An idea evoked by some experience

3. A bodily process occurring due to the effect of some antecedent stimulus or agent

4. (mechanics) the equal and opposite force that is produced when any force is applied to a body

5. A response that reveals a person's feelings or attitude

6. Extreme conservatism in political or social matters

7. Doing something in opposition to another way of doing it that you don't like