/ Dictionary / Index A aggressor: Meaning and Definition of Find definitions for: ag•gres•sor Pronunciation: (u-gres'ur), [key] — n. a person, group, or nation that attacks first or initiates hostilities; an assailant or invader. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. See also: aggressor (Thesaurus) aggressive aggrieve Related Content Daily Word Quiz: feline Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language