1. Of, on, relating to, involving, or affecting only one side: "a unilateral advantage in defense" (New Republic).
2. Performed or undertaken by only one side: unilateral disarmament.
3. Obligating only one of two or more parties, nations, or persons, as a contract or an agreement.
4. Emphasizing or recognizing only one side of a subject.
5. Having only one side.
6. Tracing the lineage of one parent only: a unilateral genealogy.
7. Botany Having leaves, flowers, or other parts on one side only.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2020 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.