WordNet records no synonym and no antonym for reaction formation. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
(psychiatry) a defense mechanism in which a person unconsciously develops attitudes and behavior that are the opposite of unacceptable repressed desires and impulses and serve to conceal them
“his strict morality is just a reaction formation to hide his sexual drive”
Synonyms, antonyms and the broader and narrower relations for reaction formation come from Princeton University’s WordNet. Full sources and licences.