Definition of: contagion

(kən·tā′jən) noun
1. The communication of disease by contact, direct or indirect, or, figuratively, of mental states by suggestion or association.
2. Pestilential influence; pestilence; plague.
3. The medium of transmission of disease; contagium. [<F <L contagio, -onis <contingere. See CONTACT.] Synonym: infection. The best usage limits contagion to diseases that are transmitted by contact with the diseased person, either directly by touch or indirectly by use of the same articles, by breath, effluvia, etc. Infection is applied to diseases produced chiefly by common climatic, malarious, or other wide–spread conditions believed to be chiefly instrumental.