1. The act or process of forming something or of taking form.
2. Something formed: beautiful cloud formations.
3. The manner or style in which something is formed; structure: the distinctive formation of the human eye.
4. A specified arrangement or deployment, as of aircraft, troops, or players on a sports team.
5. Geology A primary unit in the mapping of rock strata, consisting of a set of contemporaneous rocks having the same characteristics and origin.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2019 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.