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, n.). Psychological sense of "hostile or destructive behavior" first recorded 1912 in A.A. Brill's translation of Freud.