verb (used without object)
- to act in response to an agent or influence: How did the audience react to the speech?
- to act reciprocally upon each other, as two things.
- to act in a reverse direction or manner, especially so as to return to a prior condition.
- to act in opposition, as against some force.
- to respond to a stimulus in a particular manner: reacting to a shock by jumping; to react to the word “coward” with anger.
- to undergo a chemical reaction.
verb (used with object)
- to act or perform again.
verb
- (intr ; foll by to, upon etc) (of a person or thing) to act in response to another person, a stimulus, etc, or (of two people or things) to act together in a certain way
- (intr foll by against) to act in an opposing or contrary manner
- (intr) physics to exert an equal force in the opposite direction to an acting force
- chem to undergo or cause to undergo a chemical reaction
verb
- (tr) to act or perform again
1640s, “to exert, as a thing acted upon, an opposite action upon the agent,” from re- + act (v.). Chemical sense is from 1944. Related: Reacted; reacting (1610s). For sense development, see reaction. Meaning “perform again” (often re-act) is from 1650s.
v.
- To act in response to a stimulus.
- To undergo a chemical reaction.