infectiouscapable of causing infection; transmitted without contact: Cholera is an infectious epidemic disease caused by a microorganism.Not to be confused with:contagious ? transmissible by contact; catching; capable of carrying disease: A head cold can be contagious.Abused, Confused, & Misused Words by Mary Embree Copyright © 2007, 2013 by Mary Embreein·fec·tious (?n-f?k?sh?s)adj.1. Capable of causing infection: an infectious microorganism.2. Capable of being transmitted by infection: an infectious disease.3. Capable of transmitting a disease; contagious: Is the patient still infectious?4. Spreading or tending to spread from one to another: an infectious laugh.in·fec?tious·ly adv.in·fec?tious·ness n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.infectious (?n?f?k??s) adj1. (Medicine) (of a disease) capable of being transmitted. Compare contagious2. (Pathology) (of a disease) caused by microorganisms, such as bacteria, viruses, or protozoa3. (Medicine) causing or transmitting infection4. tending or apt to spread, as from one person to another: infectious mirth. 5. (Law) international law a. tainting or capable of tainting with illegalityb. rendering liable to seizure or forfeiture in?fectiously adv in?fectiousness nCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014in?fec?tious (?n?f?k ??s) adj. 1. communicable by infection, as from one person to another or from one part of the body to another. 2. causing or communicating infection. 3. tending to spread quickly and generally: infectious laughter. 4. Obs. diseased. [1535?45] in?fec?tious?ly, adv. in?fec?tious?ness, n. syn: See contagious. Random House Kernerman Webster’s College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.in·fec·tious (?n-f?k?sh?s) Capable of causing infection: an infectious disease.Usage A contagious or communicable disease is one that can be transmitted from one living being to another through direct or indirect contact. Thus the flu, which can be transmitted by coughing, and cholera, which is often acquired by drinking contaminated water, are contagious (or communicable) diseases. Modern medicine also uses the word infectious to refer to such diseases. Infectious has a slightly different meaning. It refers to diseases caused by infectious agents?agents such as viruses and bacteria that are not normally present in the body and can cause an infection. While the notion of contagiousness goes back to ancient times, the idea of infectious diseases is more modern, coming from the germ theory of disease, which was not proposed until the later 19th century. Contagious and infectious are also used to refer to people who have communicable diseases at a stage at which transmission to others is likely.The American Heritage® Student Science Dictionary, Second Edition. Copyright © 2014 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.