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.
-
Law. capable of contaminating with illegality; exposing to seizure or forfeiture.
-
Obsolete. diseased.
adjective
-
(of a disease) capable of being transmitted Compare contagious
-
(of a disease) caused by microorganisms, such as bacteria, viruses, or protozoa
-
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
-
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.
This protective system helps shield the brain from harmful substances, including toxins and infectious agents.
From Science Daily ● Nov. 1, 2026
This result suggests that renewable, genetically engineered immune cell progenitors might eventually have applications beyond cancer, including treatments for inherited immune deficiencies and potentially infectious diseases.
From Science Daily ● Oct. 16, 2026
Nevertheless, the author’s enthusiasm for his subjects is infectious.
From The Wall Street Journal ● Oct. 14, 2026
Such nodules "could be a whole range of benign lesions -- inflammatory, infectious, autoimmune, or congenital -- or they could be malignant," Venuta said.
From Barron's ● Oct. 13, 2026
In the end, Joe McCormick had been right about the Ebola Reston virus: it had not proved to be highly infectious in people.
From "The Hot Zone" by Richard Preston
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Get a wordDefinitions 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.
