Meaning of REACTION in English
n.1 the act or an instance of reacting; a responsive or reciprocal action.
2 a a responsive feeling (what was your reaction to the news?). b an immediate or first impression.
3 the occurrence of a (physical or emotional) condition after a period of its opposite.
4 a bodily response to an external stimulus, e.g. a drug.
5 a tendency to oppose change or to advocate return to a former system, esp. in politics.
6 the interaction of substances undergoing chemical change.
7 propulsion by emitting a jet of particles etc. in the direction opposite to that of the intended motion.
reactionist n. & adj.
Etymology: REACT + -ION or med.L reactio (as RE-, ACTION)
Oxford English vocab. Оксфордский английский словарь. 2012