contagious
Americanadjective
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capable of being transmitted by bodily contact with an infected person or object.
contagious diseases.
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carrying or spreading a contagious disease.
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tending to spread from person to person.
contagious laughter.
adjective
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(of a disease) capable of being passed on by direct contact with a diseased individual or by handling clothing, etc, contaminated with the causative agent Compare infectious
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(of an organism) harbouring or spreading the causative agent of a transmissible disease
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causing or likely to cause the same reaction or emotion in several people; catching; infectious
her laughter was contagious
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Capable of being transmitted by direct or indirect contact, as an infectious disease.
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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.
Related Words
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.
Other Word Forms
Etymology
Origin of contagious
First recorded in 1350–1400; Middle English, from Late Latin contāgiōsus, from contāgi(ō) contagion + -ōsus -ous
Explanation
You should probably postpone dinner if your date's cold is contagious — that means it's easily spread and likely to get you sick. Contagious actually evolved from contagio, the Latin phrase for “contact." Those smart ancient Romans — they figured out that the sick and contagious can pass on their plague to those they touch or get close to. So the word contagious usually sends people running. But let’s not forget that a smile or good deed can be just as infectious as a cough!
Vocabulary lists containing contagious
Wonder
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Roll of Thunder, Hear My Cry
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Common Senses: Tact, Tang ("Touch")
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
The WHO has declared the surge of the highly contagious haemorrhagic fever an international health emergency and will hold an emergency meeting on the crisis on Tuesday.
From Barron's • May 19, 2026
I think courage is contagious in this context too.
From Slate • May 18, 2026
The recent cases involve the rare and highly contagious Bundibugyo virus, which is less known than the Zaire strain responsible for several past outbreaks.
From The Wall Street Journal • May 17, 2026
While COVID-19 was airborne and far more contagious, he guesses hantavirus is 50 times more deadly.
From MarketWatch • May 14, 2026
Since everyone knows that trouble can be contagious, they were alone until Turner and his mother sat down next to them.
From "Lizzie Bright and the Buckminster Boy" by Gary D. Schmidt
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
