Q: I’ve been seeing the use of the word “reactionary” for “reactive.” Have you noticed this?
A: No, we haven’t noticed it, and none of the standard dictionaries we rely on have entries for the adjective “reactionary” that include “reactive” as a meaning.
However, the online collaborative reference Wiktionary includes this sense of “reactionary” as used in chemistry: “Of, pertaining to, participating in or inducing a chemical reaction.”
Wiktionary cites an April 11, 2013, article by Brandon Smith on Alt-Market.com, a website devoted to barter networking and other economic alternatives:
“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.”
Although the usage you’re asking about isn’t all that common, it isn’t all that new either.
The Oxford English Dictionary has citations dating back to the mid-19th century for “reactionary” used to mean “of, or relating to, or characterized by reaction, or a reaction (in various senses); that constitutes a reaction or reversal.”
The dictionary’s earliest example for this reactive sense is from an 1847 volume of A History of Greece, a 12-volume work by George Grote:
“The intensity of the subsequent displeasure would be aggravated by this reactionary sentiment.” (The reference is to how Athenians reacted when Mitliades, a hero of the Battle of Marathon, failed in the Expedition at Paros.)
In Women in Love (1920), D. H. Lawrence describes an affair as the result of—that is, a reaction to—marriage: “A liaison was only another kind of coupling, reactionary from the legal marriage. Reaction was a greater bore than action.”
Finally, here’s an OED citation (from the Feb. 6, 2003, issue of the Charlotte Business Journal in North Carolina) with the term used in the medical sense: “We want to practice preventative health care and not just reactionary medicine.”
Well, the usage is out there, as you’ve noticed, and it has a history, but it’s not out there enough to make it into standard dictionaries. In other words, you’ll probably be misunderstood if you use it.