contagious

adjective

con·​ta·​gious kən-ˈtā-jəs 

1

: transmissible by direct or indirect contact with an infected person

contagious diseases

contagious intestinal illness

contagious skin rash

contagious viruses

see also contagious disease

2

: bearing contagion

contagious people

3

: used for contagious diseases

a contagious ward

4

: exciting similar emotions or conduct in others

contagious enthusiasm

contagious laughter

contagiously adverb

contagiousness noun

Did you know?

What is the Difference Between contagious and infectious?

The words contagious and infectious can be confusing because they do not designate wholly distinct categories; something is not either contagious or infectious.

Essentially, infectious diseases and contagious diseases are caused by disease-producing agents such as bacteria and viruses, but they differ in that contagious diseases can be spread to other people by direct or indirect contact.

Anything contagious, such as the flu, is always automatically infectious: if you can catch it from someone, it's being passed to you via an infectious agent, which is the thing that gets you sick—usually a virus or a bacteria.

The reverse, however, isn't true. Just because something is infectious does not mean it's contagious. Food poisoning, for example, is infectious but not contagious: food can be contaminated with a bacteria (an infectious agent) that makes you sick, but you can't give your food poisoning to someone else by shaking their hand or even giving them a kiss.

Both contagious and infectious are also used figuratively, often in much happier contexts: laughter can be contagious; someone's enthusiasm can be infectious. While both words are used figuratively of both pleasant and unpleasant things, contagious is more often chosen for the unpleasant, as when it's grumpiness or fear that seems to be spreading.

Synonyms

• infectious
• infective

Examples of contagious in a Sentence

It's a highly contagious virus.

I have a cold and I'm still contagious.

I'm sick, but the doctor says I'm not contagious.

Recent Examples on the Web

When leaders respond from center, their presence becomes contagious. —Ashley B. Stewart, Forbes.com, 8 July 2025

Over the weekend, the tally of measles cases reached 1,281, setting a new case record since the highly contagious viral disease was declared eliminated from the country in 2000. —ArsTechnica, 7 July 2025

Because the measles virus can remain in the air and on surfaces for up to two hours and is highly contagious, anyone who was a patient, staff member, or visitor to the unit during that period may have been exposed. —Kansas City Star, 7 July 2025

Measles ranks among the most contagious infectious diseases, with 92 percent of unvaccinated people contracting the virus upon exposure. —Adeola Adeosun, MSNBC Newsweek, 6 July 2025

Word History

Etymology

Middle English, "contaminating, communicable," borrowed from Anglo-French & Late Latin; Anglo-French, borrowed from Late Latin contāgiōsus, from Latin contāgiō "contact, contagion" + -ōsus -ous

First Known Use

14th century, in the meaning defined at sense 1

Phrases Containing contagious

• contagious abortion
• contagious disease

Rhymes for contagious

• advantageous
• courageous
• outrageous
• disadvantageous

Kids Definition

contagious

adjective

con·​ta·​gious kən-ˈtā-jəs 

1

a

: able to be passed on by contact between individuals

colds are contagious

contagious diseases

b

: capable of passing on a contagious disease to another

he is contagious

2

: so pleasantly irresistible as to be picked up by one person after another

your enthusiasm is contagious

Etymology

Middle English contagious "likely to be passed on through contact," from early French contagieus (same meaning), derived from Latin contingere "to have contact with, affect, happen" — related to contact, contingent

Medical Definition

contagious

adjective

con·​ta·​gious -jəs 

1

: communicable by contact

tuberculosis in the contagious stage

2

: bearing contagion

many persons … are contagious long before they are aware of the presence of their disease

—The Journal of the American Medical Association

3

: used for contagious diseases

a contagious ward

contagiously adverb

contagiousness noun