1. Not formal or ceremonious; casual: an informal gathering of friends; a relaxed, informal manner.
2. Not being in accord with prescribed regulations or forms; unofficial: an informal agreement.
3. Suited for everyday wear or use: informal clothes.
4. Characterized by nontechnical vocabulary, simple sentence structure, and relatively few explicit transitions, as typified by spoken language: informal discourse.
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.