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."

influenzal

ˌin-(ˌ)flü-ˈen-zəl 

adjective

influenzal pneumonia

influenzal symptoms

Examples of influenza in a Sentence

Recent Examples on the Web

Human transmission of influenza A virus is very rare, the CDC said. —Lauren De Young, The Arizona Republic, 12 Dec. 2024

Teen in Critical Condition After Contracting Canada's First ‘Presumptive’ Human Case of Bird Flu Symptoms of bird flu mimic those associated with influenza, according to the CDC: fever, fatigue, cough, muscle aches, sore throat, shortness of breath, stuffy or runny nose, eye redness, and headaches. —Cara Lynn Shultz, People.com, 11 Dec. 2024

Flu Shot: Get an annual flu shot to stay protected against the ever-changing strains of seasonal influenza. —Sandra Rose Salathe, Flow Space, 9 Dec. 2024

Seasonal influenza typically has a case fatality ratio well below 1%. —Dave Wessner, Forbes, 8 Dec. 2024

Word History

Etymology

Italian, literally, influence, from Medieval Latin influentia; from the belief that epidemics were due to the influence of the stars

First Known Use

1743, in the meaning defined at sense 1a

Phrases Containing influenza

• avian influenza
• swine influenza

Kids 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."

influenzal

-zəl 

adjective

influenzal pneumonia

influenzal symptoms