react

Etymology

From re- + act.

verb

1. (intransitive) To act in response.
   How did she react to the news?
2. (transitive, now rare) 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. 1791, Thomas Paine, Rights of Man
3. (physics, 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. (chemistry, 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. (chemistry, 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