reactionary

Etymology

From French réactionnaire. Used in the time of the French revolution to refer to a person opposing the revolution; as in a person favoring a reaction to the revolution. First known usage in English in a translation of Lazare Carnot's letter on the Conspiracy of the 18th Fructidor published in London, 1799.

adj

1. (politics) Favoring a return to an alleged golden age of the past; anti-progressive.
   There's a fairly simple reason for the embrace of radicalism on the right, and it has to do with the reactionary imperative that lies at the core of conservative doctrine. […] If he is to preserve what he values, the conservative must declare war against the culture as it is. 2011-09-29, Corey Robin, The Reactionary Mind: Conservatism from Edmund Burke to Sarah Palin, New York: Oxford University Press, →OL, page 25
   [Jeffrey] Epstein was interested in transhumanism, a theory of human perfection via technological manipulation that—like its predecessor, eugenics—is shot through with racist and reactionary ideas. 2019-8-7, Marissa Brostoff, Noah Kulwin, “The Right Kind of Continuity”, in Jewish Currents
2. (chemistry) Of, pertaining to, participating in, or inducing a chemical reaction.
   Psychiatry extends the theory into biology in the belief that all human behavior is nothing more than a series of reactionary chemical processes in the brain that determine pre-coded genetic responses built up from the conditioning of one’s environment. 2013, Brandon Smith, Are Individuals The Property Of The Collective?
3. In reaction to; as a result of.
   The regulator noted that reduced service levels and passenger numbers helped deliver strong performance, with fewer reactionary delays. December 16 2020, “Network News: ORR praises Network Rail's response to pandemic”, in Rail, page 13

noun

1. (politics) One who is opposed to progress and change and wants to reverse it, wishing for a return to an alleged golden age of the past.
   Hindu reactionaries, whose conception of a well-ordered society had not moved beyond the laws of Manu, fell into line for the moment with the intellectual products of the modern Indian University. 1921, Valentine Chirol, India, Old and New
   It is not simply a conservative preference for things as they are, with a few nudges back, but a passionate loathing of the status quo and a desire to return to the past in one emotionally cathartic revolt. If conservatives are pessimistic, reactionaries are apocalyptic. 2017 April, Andrew Sullivan, “The Reactionary Temptation”, in New York [Magazine]