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

If everyone you know seems to have the flu, there is a reason for that: Influenza climbed to unusually high levels across the country, thanks to a flu strain that caught us off guard.

From The Wall Street Journal • Jan. 12, 2026

Influenza continues to place a heavy burden on health systems worldwide.

From Science Daily • Jan. 11, 2026

Influenza, which can cause falls and cognitive status issues in older people during acute infection and recovery, offers a classic example.

From Salon • Jul. 12, 2025

The Avian Influenza Prevention Zone across England applies to all keepers of birds, be they pets or commercial flocks.

From BBC • Jan. 25, 2025

Do you think that they, with their Battles, Famine, Black Death and Serfdom, were less enlightened than we are, with our Wars, Blockade, Influenza and Conscription?

From "The Once and Future King" by T. H. White

Related Words

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