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1610s, "unprovoked attack," from French aggression (16c.), from Latin aggressionem (nominative aggressio) "a going to, an attack," noun of action from past participle stem of aggredi "to approach; attack," from ad- "to" (see ad-) + gradi (past participle gressus) "to step," from gradus "a step" (see grade). Psychological sense of "hostile or destructive behavior" first recorded 1912 in A.A. Brill's translation of Freud.
aggression ag·gres·sion (ə-grěsh'ən)
Hostile or destructive behavior or actions.