flu
Americannoun
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a specific variety of influenza, usually named for its point of dissemination or its animal vector.
Hong Kong flu; swine flu.
noun
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short for influenza
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any of various viral infections, esp a respiratory or intestinal infection
Etymology
Origin of flu
First recorded in 1830–40; shortened form
Compare meaning
How does flu compare to similar and commonly confused words? Explore the most common comparisons:
Explanation
The flu is a disease that's easily spread between people. When you have body aches, a fever, and a sore throat, you probably have the flu. The word flu is shorthand for "influenza," the official name of this infectious, viral illness. It's not unusual to get the flu, especially in the winter, and while it usually isn't serious, it can be deadly for some groups of people. Your chances of getting the flu are greatly reduced if you get a flu shot. The Italian root influenza means "influenza" or "epidemic," but also "visitation" or "influence of the stars."
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.
What is freshers' flu - and why do so many get it?
From BBC ● Aug. 15, 2026
Typically, those ailments — think flu and respiratory syncytial virus — spike in the winter, and aren’t really seen outside of that season.
From Los Angeles Times ● Aug. 14, 2026
But those for hepatitis A and B, dengue, flu, Covid and rotavirus would be advised only for “high-risk” children, or else would to be left to “shared clinical decision-making” between doctors and parents.
From The Wall Street Journal ● Aug. 11, 2026
This isn’t a pandemic anymore, according to experts, but that’s because the virus is now endemic — it’s a part of our daily lives like flu, HIV and other infectious diseases.
From Salon ● Aug. 6, 2026
“This old movie, Guess Who. I caught it when I had the flu a few weeks ago. Zoe Saldana dated Ashton Kutcher. Her dad didn’t like that she was seeing a white guy. That’s us.”
From "The Hate U Give" by Angie Thomas
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.
