react

verb

1. (intransitive)To act in response.

   “How did she react to the news?”

2. (archaic, transitive)To act or perform a second time; to do over again; to reenact.

   “It is somewhat extraordinary, that the offence for which James II, was expelled, that of setting up power by assumption, should be re-acted, under another shape and form, by the parliament that expelled him.”

3. (intransitive)To return an impulse or impression; to resist the action of another body by an opposite force

   “Every body reacts on the body that impels it from its natural state.”

4. (intransitive)To act upon each other; to exercise a reciprocal or a reverse effect, as two or more chemical agents; to act in opposition.
5. (transitive)To cause chemical agents to react; to cause one chemical agent to react with another.
6. (Internet, intransitive)To post a reaction (icon or emoji indicating how one feels about a posted message).

noun

1. (Internet)An emoji used to express a reaction to a post on social media.

   “Sad reacts only”