a. Disease transmission by direct or indirect contact.
b. A disease that is or may be transmitted by direct or indirect contact; a contagious disease.
c. The direct cause, such as a bacterium or virus, of a communicable disease.
2. Psychology The spread of a behavior pattern, attitude, or emotion from person to person or group to group through conscious or unconscious imitation.
3. A harmful, corrupting influence: feared that violence on television was a contagion affecting young viewers.
4. The tendency to spread, as of a doctrine, influence, or emotional state.
[Middle English contagioun, from Latin contāgiō, contāgiōn-, from contingere, contāct-, to touch; see CONTACT.]
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.