infectious
Americanadjective
-
communicable by infection, as from one person to another or from one part of the body to another.
infectious diseases.
- Synonyms:
- catching
-
causing or communicating infection.
-
tending to spread from one to another.
infectious laughter.
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Law. capable of contaminating with illegality; exposing to seizure or forfeiture.
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Obsolete. diseased.
adjective
-
(of a disease) capable of being transmitted Compare contagious
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(of a disease) caused by microorganisms, such as bacteria, viruses, or protozoa
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causing or transmitting infection
-
tending or apt to spread, as from one person to another
infectious mirth
-
international law
-
tainting or capable of tainting with illegality
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rendering liable to seizure or forfeiture
-
Synonym Usage
See contagious.
Other Word Forms
Etymology
Origin of infectious
First recorded in 1535–45; infect(ion) + -ious
Explanation
Infectious means able to be spread by infection, like a disease that spreads from one person to another. You'll be uncomfortable shaking Uncle Marvin's hand if you're worried that warts are infectious. Something that's infectious spreads easily, like infectious cold germs that might be left on a door handle — anyone who touches it might get sick. If your mother tells you the cut on your knee looks infectious, you'd better go to the doctor. Some infectious things are good — like infectious laughter that gets the whole class giggling, or your friend's infectious good mood that makes you forget your cares.
Vocabulary lists containing infectious
"Romeo and Juliet" by William Shakespeare, Act V
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National Nurses Week: Common Medical Terms
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An American Plague
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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.
"No health disorders associated with infectious pathology were detected," it said, adding that "the results of almost 5,000 laboratory tests did not reveal any dangerous pathogenic microorganisms".
From Barron's ● Oct. 7, 2026
An international conference on plague and other infectious diseases will meanwhile be held in Irkutsk on October 21-22.
From Barron's ● Oct. 6, 2026
Russian authorities are investigating the death of a woman who worked at a Siberian institute for infectious diseases and have placed her contacts under close medical observation as they try to determine how she died.
From The Wall Street Journal ● Oct. 5, 2026
He added: "But of course people's thought with any outbreak of infectious disease at all runs to... lockdowns and Covid and that is just not what's going to happen here."
From BBC ● Oct. 5, 2026
Both involved quarantines—the practice of isolating someone with a highly infectious disease from the healthy population.
From "Mountains Beyond Mountains" by Tracy Kidder and Michael French
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.
