(1):

(n.) That which serves as a medium or agency to transmit disease; a virus produced by, or exhalation proceeding from, a diseased person, and capable of reproducing the disease.

(2):

(n.) The transmission of a disease from one person to another, by direct or indirect contact.

(3):

(n.) The act or means of communicating any influence to the mind or heart; as, the contagion of enthusiasm.

(4):

(n.) Venom; poison.