Dictionaries vary in their definition. Webster’s Ninth NewCollegiate Dictionary defines aggression as:
(1) a forceful action of procedure (as an unprovoked attack) esp. when intended to dominate or master; (2) the practice of making attacks or encroachments; esp. unprovoked violations by one country of the territorial integrity of another; (3) hostile, injurious, or destructive behaviour or outlook esp. when caused by frustration.
The Concise Oxford Dictionary defines aggression as an ‘act of beginning a quarrel or war; unprovoked attack; (Psych) hostile or destructive tendency or behaviour’.
Early research definitions also varied. Dollard et al. (1939 p. 11) described angry aggression as ‘an act whose goal-response is injury to another organism’. Dollard and colleagues suggested that the motivation of the ‘goal-response’ is to cause harm such that aggression is perceived as the end behaviour of a motivated sequence of behaviours. The achievement of the goal is realized by the victim’s overt suffering through some expression of pain. This definition neglected to address the motivation of receiving a reward for the aggressive behaviour, such as a father reinforcing his son for winning a fight. It also limited the definition to the intentional delivery of noxious stimuli as distinct from impulsive or irrational actions.