defense mechanism [L, defendere, to repulse, mechanicus, machine; from the psychoanalytic theory of Sigmund Freud, Czech-Austrian neurologist and psychiatrist, 1856−1939] , an unconscious intrapsychic reaction that offers protection to the self from stress or a threat. Defense mechanisms are of two types: those that diminish anxiety and are used by an individual to integrate more fully into society and those that do not reduce anxiety but simply postpone the effects of feeling it. Anxiety-reducing defenses include compensation, identification, introjection, some forms of repression, and sublimation. Defenses that postpone full expression of anxiety include denial, displacement, isolation, projection, reaction formation, rationalization, regression, some forms of repression, suppression, and undoing.
