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.
They come on suddenly and start like the flu, with fever, headache and tiredness.
From BBC • May 18, 2026
People infected by the Bundibugyo strain initially show symptoms similar to flu or malaria which can delay detection.
From Barron's • May 18, 2026
There have been nine such declarations, including the Ebola outbreak in 2013, the COVID-19 pandemic, and the swine flu pandemic in 2009.
From MarketWatch • May 17, 2026
In many states, for example, pharmacists now prescribe medications such as contraceptives and flu treatments.
From The Wall Street Journal • May 16, 2026
“Miss Taylor is out sick with the flu, so today I’m going to be your teacher.”
From "The Lions of Little Rock" by Kristin Levine
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.
