Definition of "infectious" []

• Capable of causing infection. (adjective)
• Caused by or capable of being transmitted by infection. (adjective)
• Caused by a pathogenic microorganism or agent. (adjective)
• Easily or readily communicated: an infectious laugh. (adjective)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "BLITZER: It brings new meaning to the term infectious enthusiasm."
• "Technically speaking, when you hear a veterinarian speaking of the condition, you will hear the term infectious tracheobronchitis."
• "This general result I shall only support by the authority of Dr. Ramsbotham, who gives, as the result of his experience, that the same symptoms belong to what he calls the infectious and the sporadic forms of the disease, and the opinion of Armstrong in his original Essay."