1. Psychology In psychoanalytic theory, any of various usually unconscious mental processes, including denial, projection, rationalization, and repression, that protect the ego from shame, anxiety, conflict, loss of self-esteem, or other unacceptable feelings or thoughts.
2. Biology A physiological reaction of an organism used in self-protection, as against infection.
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.