capable of being transmitted by bodily contact with an infected person or object: contagious diseases.
carrying or spreading a contagious disease.
tending to spread from person to person: contagious laughter.
Origin of contagious
1350–1400;Middle English < Late Latincontāgiōsus, equivalent to contāgi(ō) contagion + -ōsus-ous
Related formscon·ta·gious·ly, adverbcon·ta·gious·ness, con·ta·gi·os·i·ty[kuh n-tey-jee-os-i-tee]/kənˌteɪ dʒiˈɒs ɪ ti/, nounan·ti·con·ta·gious, adjectivean·ti·con·ta·gious·ly, adverban·ti·con·ta·gious·ness, nounnon·con·ta·gious, adjectivenon·con·ta·gious·ly, adverbnon·con·ta·gious·ness, nounun·con·ta·gious, adjectiveun·con·ta·gious·ly, adverbCan be confusedcontagiousinfectious (see synonym study at the current entry)
1. Contagious,infectious are usually distinguished in technical medical use. Contagious, literally “communicable by contact,” describes a very easily transmitted disease as influenza or the common cold. Infectious refers to a disease involving a microorganism that can be transmitted from one person to another only by a specific kind of contact; venereal diseases are usually infectious. In nontechnical senses, contagious emphasizes the rapidity with which something spreads: Contagious laughter ran through the hall.Infectious suggests the pleasantly irresistible quality of something: Her infectious good humor made her a popular guest.
Capable of being transmitted by direct or indirect contact, as an infectious disease.
Bearing contagion, as a person or animal with an infectious disease that is contagious.
Usage: A contagious 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 diseases. Although infectious is also used to refer to such diseases, it has a slightly different meaning in that 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 nineteenth 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.