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.
Flu vaccines are a major business for Sanofi, whose products are widely administered as part of annual national vaccination campaigns in France in particular.
From Barron's • Jun. 26, 2026
It is not yet clear whether the new H3N2 Flu A subclade K subvariant will reduce the efficacy of the flu vaccine this season.
From Los Angeles Times • Feb. 27, 2026
Appeared in the February 19, 2026, print edition as 'A Welcome Walkback on a Flu Vaccine'.
From The Wall Street Journal • Feb. 18, 2026
Flu hit early this winter with a new mutated version of the virus circulating.
From BBC • Jan. 8, 2026
I was sorry to see by your note in pencil yesterday that you were in bed with "Flu."
From Letters of Lt.-Col. George Brenton Laurie (commanding 1st Battn. Royal Irish Rifles) Dated November 4th, 1914-March 11th, 1915 by Vere-Laurie, Florence
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.
