1a. Hostile or destructive behavior or attitudes: physical aggression ; verbal aggression ; emotional aggression. b. Forceful, assertive, or overbearing behavior or. It's been used since the s to mean "an unprovoked attack," from the Latin root word aggressionem, "attack," and in aggression was first used to mean. aggression meaning, definition, what is aggression: spoken or physical behaviour that is threatening or involves harm to someone or. Learn more.