1. aggressive or submissive behavior in response to real or imagined threats of harm. A cat, for example, may exhibit defensive aggression by spitting and hissing, arching its back, and raising the hair along the back of the neck in anticipation of a physical threat (see animal defensive behavior). A human might fend off criticism by putting forth self-justifying excuses or by expressing an emotional reaction (e.g., crying) to limit another’s disapproval or anger.

2. in psychoanalytic theory, behavior characterized by the use or overuse of defense mechanisms operating at an unconscious level.