n. Disease transmission by direct or indirect contact.n. A disease that is or may be transmitted by direct or indirect contact; a contagious disease.n. The direct cause, such as a bacterium or virus, of a communicable disease.n. Psychology The spread of a behavior pattern, attitude, or emotion from person to person or group to group through suggestion, propaganda, rumor, or imitation.n. A harmful, corrupting influence: feared that violence on television was a contagion affecting young viewers. n. The tendency to spread, as of a doctrine, influence, or emotional state.