reaction

noun

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

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?”

2. 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. Reactionary politics; a period in which reactionary thought or politics is resurgent or dominant.

   “And as Europe advanced year by year more deeply into the low featureless plains of reaction, censorship and mediocrity and the pestilential swamps of poverty, unhappiness and oppression, the image of the liberating revolution became ever more luminous.”

4. Unpurposeful behavior.
5. An icon or emoji appended to a posted message by a user to express their feeling about it.