Pronunciation: (u-gres'iv),[key] —adj. 1. characterized by or tending toward unprovoked offensives, attacks, invasions, or the like; militantly forward or menacing: aggressive acts against a neighboring country. 2. making an all-out effort to win or succeed; competitive: an aggressive basketball player. 3. vigorously energetic, esp. in the use of initiative and forcefulness: an aggressive salesperson. 4. boldly assertive and forward; pushy: an aggressive driver. 5. emphasizing maximum growth and capital gains over quality, security, and income: an aggressive mutual fund. 6. using daring or forceful methods: aggressive treatment of infection.