reaction

Etymology

Old French reaction, from Latin reāctiō, from the verb reagō, from re- (“again”) + agō (“to act”); more at re-, action; equivalent to react + -ion.

noun

1. An action or statement in response to a stimulus or other event.
   The announcement of the verdict brought a violent reaction.
   You were in the courtroom. What is your reaction?
   When I last tried to eat strawberries I had a terrible allergic reaction.
2. (chemistry) A transformation in which one or more substances is converted into another by combination or decomposition.
   In this reaction, the acid and base will neutralize each other, producing a salt.
3. (politics) Reactionary politics; a period in which reactionary thought or politics is resurgent or dominant.
4. (Internet) An icon or emoji appended to a posted message by a user to express their feeling about it.