con·ta·gion (kən-tāˈjən)

1. Disease transmission by direct or indirect contact.
2. A disease that is or may be transmitted by direct or indirect contact; a contagious disease.
3. The direct cause, such as a bacterium or virus, of a communicable disease.
4. The spread of a behavior pattern, attitude, or emotion from person to person or group to group through suggestion, propaganda, rumor, or imitation.