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.
That translates to the flu season landing about seven weeks earlier than in 2025 or 2024.
From MarketWatch ● Oct. 9, 2026
The mFLUSIVA vaccine is more effective than other flu shots, although it comes with more side effects, which are similar to what people experience with Moderna’s COVID-19 vaccine.
From MarketWatch ● Oct. 9, 2026
Compared with other illnesses, the plague isn’t much of a problem these days: Each year the regular old flu kills many thousands of people in the United States alone.
From Slate ● Oct. 8, 2026
More patients, including children, have been arriving at A&E departments with flu and other respiratory viruses.
From BBC ● Oct. 8, 2026
Nobody gossips about whether you have the flu or not.
From "Ask the Passengers" by A.S. King
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.
