contagious

American  

[kuhn-tey-juhs] / kənˈteɪ dʒəs /

adjective

1. capable of being transmitted by bodily contact with an infected person or object.

   contagious diseases.

2. carrying or spreading a contagious disease.

3. tending to spread from person to person.

   contagious laughter.

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contagious British  

/ kənˈteɪdʒəs /

adjective

1. (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

2. (of an organism) harbouring or spreading the causative agent of a transmissible disease

3. causing or likely to cause the same reaction or emotion in several people; catching; infectious

   her laughter was contagious

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contagious Scientific  

/ kən-tā′jəs /

1. Capable of being transmitted by direct or indirect contact, as an infectious disease.

2. Bearing contagion, as a person or animal with an infectious disease that is contagious.

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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

• anticontagious adjective
• anticontagiously adverb
• anticontagiousness noun
• contagiosity noun
• contagiously adverb
• contagiousness noun
• noncontagious adjective
• noncontagiously adverb
• noncontagiousness noun
• uncontagious adjective
• uncontagiously adverb

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!

Example Sentences

And discontent can be contagious, ultimately having a ripple effect on worsening morale and productivity.

From Slate • Apr. 20, 2026

Measles is a highly contagious airborne disease, which can lead to severe complication and death.

From BBC • Apr. 6, 2026

But the contagious nature of the band’s biggest singles has, over time, earned them a fortified respect for the legacy.

From Salon • Apr. 4, 2026

The virus is so contagious that any misstep could kill the patient on board and infect the crew members, who would then be vectors to spread the deadly pathogens across America.

From The Wall Street Journal • Mar. 20, 2026

The admiral’s sense of adventure was as contagious as a bad pun, and Penelope was starting to feel the effects herself.

From "The Unseen Guest" by Maryrose Wood

Related Words

• deadly
• endemic
• infectious
• poisonous
• spreading