1. Characterized by aggression: aggressive behavior.
2. Inclined to behave in an actively hostile fashion: an aggressive regime.
3. Assertive, bold, and energetic: an aggressive sales campaign.
4. Of or relating to an investment or approach to investing that seeks above-average returns by taking above-average risks.
5. Fast growing; tending to spread quickly and invade: an aggressive tumor.
6. Characterized by or inclined toward vigorous or intensive medical treatment: an aggressive approach to treating the infection.
7. Intense or harsh, as in color.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.