influenza

American  

[in-floo-en-zuh] / ˌɪn fluˈɛn zə /

noun

1. Pathology. an acute, commonly epidemic disease, occurring in several forms, caused by numerous rapidly mutating viral strains and characterized by respiratory symptoms and general prostration.

2. Veterinary Pathology. an acute, contagious disease occurring in horses and swine, characterized by fever, depression, and catarrhal inflammations of the eyes, nasal passages, and bronchi, and caused by a virus.

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influenza British  

/ ˌɪnflʊˈɛnzə /

noun

1. Also called: grippe.   flu.  informal a highly contagious and often epidemic viral disease characterized by fever, prostration, muscular aches and pains, and inflammation of the respiratory passages

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influenza Scientific  

/ ĭn′flo̅o̅-ĕn′zə /

1. A highly contagious infectious disease that is caused by any of various viruses of the family Orthomyxoviridae and is characterized by fever, respiratory symptoms, fatigue, and muscle pain. It commonly occurs in epidemics, one of which killed 20 million people between 1917 and 1919.

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influenza Cultural  

1. Commonly called the flu; an acute and infectious disease of the respiratory system caused by a virus and characterized by fever, muscle pain, headache, and inflammation of the mucous membranes in the respiratory tract.

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Word History

Since ancient times, influenza has periodically swept the world. Until recently, people could not tell how this illness, which we call the flu, could spread so widely. Before people knew that organisms cause disease, they thought the stars influenced the spread of influenza. Influenza comes ultimately from the Latin word influentia, meaning “influence of the stars.” Today, however, the stars are no longer blamed for the flu. Inhaling influenza viruses causes the spread of the illness.

Other Word Forms

• influenzal adjective
• influenzalike adjective
• postinfluenzal adjective

Etymology

Origin of influenza

1735–45; < Italian < Medieval Latin influentia influence

Compare meaning

How does influenza compare to similar and commonly confused words? Explore the most common comparisons:

• parainfluenza vs. influenza

Explanation

An influenza is a contagious viral infection. Influenzas tend to spread during the winter, and they're more commonly known as the flu. If you've ever wondered why this word looks so much like influence, that’s because both come from the Italian influentia. The original idea was a flowing in — of ethereal fluid from the heavens, thus affecting human destiny. We know now influenza is caused by viruses, not heavenly fluid. When you have an influenza, you're likely to vomit, have diarrhea, be exhausted, and feel terrible overall. One way to prevent influenza is by getting a flu shot.

Example Sentences

The Centers for Disease Control and Prevention currently classifies the U.S. influenza season, which usually runs from October to May, as “moderate severity.”

From Barron's • Apr. 16, 2026

What has helped is that the threat of highly pathogenic avian influenza, or bird flu, has faded.

From MarketWatch • Apr. 1, 2026

More than 50 skuas died in Antarctica during the summers of 2023 and 2024 after becoming infected with the highly pathogenic avian influenza virus H5N1.

From Science Daily • Feb. 12, 2026

Moderna, a pioneer of mRNA technology, asked the FDA to approve its experimental, mRNA-based vaccine to protect against seasonal influenza in early January, the company said.

From The Wall Street Journal • Feb. 10, 2026

Death stalked the congress in the form of influenza.

From "1491" by Charles C. Mann

Related Words

• contagion
• curse
• epidemic
• infection
• infestation
• invasion
• outbreak
• pandemic
• scourge