1610s, "unprovoked attack," from French aggression (16c., Modern French agression), from Latin aggressionem (nominative aggressio) "a going to, an attack," noun of action from past-participle stem of aggredi "to approach; to attempt; to attack," from ad "to" (see ad-) + gradi (past participle gressus) "to step," from gradus "a step," figuratively "a step toward something, an approach" (from PIE root *ghredh- "to walk, go"). Psychological sense of "hostile or destructive behavior" first recorded 1912 in A.A. Brill's translation of Freud.
