influenza
noun
in·flu·en·za
ˌin-(ˌ)flü-ˈen-zə 
1
a
: an acute, highly contagious, respiratory disease caused by any of three orthomyxoviruses:
(1)
or influenza A
: moderate to severe influenza that in humans is marked especially by sudden onset, fever, sore throat, fatigue, muscle aches, inflammation of the respiratory mucous membranes, and cough, that has numerous variants caused by subtypes (such as H1N1, H2N2, or H3N2) of an orthomyxovirus (species Influenza A virus of the genus Influenzavirus A) infecting humans and various animals (such as birds or pigs), and that may occur in seasonal epidemics or sometimes pandemics following mutation in the causative virus
(2)
or influenza B
: influenza with less severe symptoms that is caused by an orthomyxovirus (species Influenza B virus of the genus Influenzavirus B) infecting only humans and especially children and that may occur in seasonal epidemics but not pandemics
(3)
or influenza C
: mild influenza that is often asymptomatic, is caused by an orthomyxovirus (species Influenza C virus of the genus Influenzavirus C) infecting only humans, and does not occur in epidemics or pandemics
b
: any of various human respiratory infections of undetermined cause
—not used technically
2
: any of various virus diseases of domestic animals marked especially by fever, respiratory symptoms, and inflammation of mucous membranes
Note: All types of influenza are commonly called "the flu."
Examples of influenza in a Sentence
Recent Examples on the Web
If the influenza virus has caused pneumonia, antiviral medications, such as Tamiflu (oseltamivir) and Relenza (zanamivir), can help ease symptoms.
—
Mark Gurarie, Verywell Health, 30 Oct. 2024
But while flu is caused by influenza viruses only, a cold can be caused by more than 200 different viruses, according to Davis.
—Juno Demelo, Glamour, 25 Oct. 2024
At the same time, the U.S. is preparing for flu season, when circulation of common influenza viruses increases in fall and winter.
—Evan Bush, NBC News, 22 Oct. 2024
Compared with other influenzas, this pandemic was peculiar.
—Discover Magazine, 7 Sep. 2024
See all Example Sentences for influenza 
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Mark Gurarie, Verywell Health, 30 Oct. 2024
But while flu is caused by influenza viruses only, a cold can be caused by more than 200 different viruses, according to Davis.
—Juno Demelo, Glamour, 25 Oct. 2024
At the same time, the U.S. is preparing for flu season, when circulation of common influenza viruses increases in fall and winter.
—Evan Bush, NBC News, 22 Oct. 2024
Compared with other influenzas, this pandemic was peculiar.
—Discover Magazine, 7 Sep. 2024
See all Example Sentences for influenza
Articles Related to influenza
Dictionary Entries Near influenza
Cite this Entry
“Influenza.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/influenza. Accessed 22 Nov. 2024.
Copy CitationKids Definition
influenza
noun
in·flu·en·za
ˌin-(ˌ)flü-ˈen-zə
1
: a very contagious virus disease with fever, exhaustion, severe aches and pains, and inflammation of the respiratory tract
2
: any of various diseases of human beings or domestic animals that are usually caused by viruses and are typically marked by fever and respiratory symptoms
Etymology
from Italian influenza, literally "influence," from Latin influentia "influence," derived from earlier influere "to flow in," from in- "in, into" and fluere "to flow"
Word Origin
Originally the Italian word influenza meant what the similar-sounding word in English, influence, means: "the act or power of producing an effect indirectly." But it also had the Latin meaning of "an invisible fluid through which the stars and planets control and direct the earth and things and people on it." When epidemics raged through Europe, no one knew what the real cause was. People blamed them on evil stars working through the invisible fluid, or influence. For this reason the Italians called the disease influenza. In 1743 an epidemic very much like our modern flu began in Rome and spread. That was when the Italian word was borrowed into English. Flu is a shortened form of influenza.
Medical Definition
influenza
noun
in·flu·en·za
ˌin-(ˌ)flü-ˈen-zə
1
a
: an acute, highly contagious, respiratory disease caused by any of three orthomyxoviruses:
(1)
or influenza A
: moderate to severe influenza that in humans is marked especially by sudden onset, fever, sore throat, fatigue, muscle aches, inflammation of the respiratory mucous membranes, and cough, is caused by any of several subtypes (such as H1N1, H2N2, or H3N2) of an orthomyxovirus (species Influenza A virus of the genus Influenzavirus A) infecting humans and various animals (such as birds or pigs), and may occur in seasonal epidemics or sometimes pandemics following mutation of the causative virus see asian flu, avian influenza, bird flu, hong kong flu, spanish flu, swine flu, swine influenza
(2)
or influenza B
: influenza with less severe symptoms that is caused by an orthomyxovirus (species Influenza B virus of the genus Influenzavirus B) infecting only humans and especially children and that may occur in seasonal epidemics but not pandemics
(3)
or influenza C
: mild influenza that is often asymptomatic, is caused by an orthomyxovirus (species Influenza C virus of the genus Influenzavirus C) infecting only humans, and does not occur in epidemics or pandemics
b
: any human respiratory infection of undetermined cause
—not used technically
2
: any of various viral diseases of domestic animals (as shipping fever of horses) marked especially by fever, respiratory symptoms, and inflammation of mucous membranes
Note: All types of influenza are commonly called "the flu."
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