Noun
(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
Source: WordNetLet me formulate the artistic disposition as follows: it is reacting with one's ideal to the flaw in oneself and in the world, and somehow making that reaction formation solid enough in the medium so that it indeed becomes an improved bit of real world for others. Paul Goodman
his strict morality is just a reaction formation to hide his sexual drive Source: Internet