definition of
reaction

[1] #1 reaction n. [chemical reaction] (chemistry) a process in which one or more substances are changed into others; "there was a chemical reaction of the lime with the ground water". wn

[2] #2 reaction n. an idea evoked by some experience; "his reaction to the news was to start planning what to do". wn

[3] #3 reaction n. [response] a bodily process occurring due to the effect of some antecedent stimulus or agent; "a bad reaction to the medicine"; "his responses have slowed with age". wn

[4] #4 reaction n. (mechanics) the equal and opposite force that is produced when any force is applied to a body; "every action has an equal and opposite reaction". wn

[5] #5 reaction n. a response that reveals a person's feelings or attitude; "he was pleased by the audience's reaction to his performance"; "John feared his mother's reaction when she saw the broken lamp". wn