Hostility is seen as form of emotionally charged aggressive behavior. In everyday speech it is more commonly used as a synonym for anger and aggression.
It appears in several psychological theories. For instance it is a facet of neuroticism in the NEO PI, and forms part of personal construct psychology, developed by George Kelly.
A persistent hostile, aggressive attitude keeps the body in a permanent state of stress and overtaxes the adrenal glands. Excessive adrenalin in the blood causes circulatory problems.
It is not proven that chronic hostility, a cynical, suspicious temperament and explosive anger are related to early death and heart disease, as is popularly claimed. Several contradictory studies also exist which fail to find such a relationship.