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
Example Sentences
Recent Examples on the Web Initial theories of cause were based on a similar concept seen from other viruses such as the influenza virus, which have been known to either alter or knock out olfactory (nerve responsible for sense of smell) nerve fibers. 
Nina Shapiro, Forbes, 16 June 2022 Avian influenza viruses are classified into two groups: Low Pathogenic Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI). Orlando Mayorquin, USA TODAY, 29 Apr. 2022 Unlike influenza viruses, which mutate almost constantly, this one did not. Arianna Lapenne, CNN, 7 Aug. 2021 Viruses constantly mutate, especially if their genetic material contains ribonucleic acid (RNA), as is the case with coronaviruses and influenza viruses. Caroline Delbert, Popular Mechanics, 2 Aug. 2021 Covid-19, to be sure, but also Zika, dengue fever, novel influenza viruses, Ebola, antibiotic-resistant superbugs, and more. David Blumenthal, STAT, 23 May 2021 But the end of this piece clarifies the meaning of this coronavirus potentially joining the ranks of influenza viruses. Robin Lloyd, Scientific American, 19 Mar. 2021 In the case of influenza A, the genome is broken into eight separate segments. William A. Haseltine, Forbes, 12 Aug. 2022 Dog adoptions have been temporarily halted at the Greater Birmingham Humane Society as part of the organization’s effort to contain a canine influenza outbreak in the area. Howard Koplowitz | Hkoplowitz@al.com, al, 26 July 2022 See More
Nina Shapiro, Forbes, 16 June 2022 Avian influenza viruses are classified into two groups: Low Pathogenic Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI). Orlando Mayorquin, USA TODAY, 29 Apr. 2022 Unlike influenza viruses, which mutate almost constantly, this one did not. Arianna Lapenne, CNN, 7 Aug. 2021 Viruses constantly mutate, especially if their genetic material contains ribonucleic acid (RNA), as is the case with coronaviruses and influenza viruses. Caroline Delbert, Popular Mechanics, 2 Aug. 2021 Covid-19, to be sure, but also Zika, dengue fever, novel influenza viruses, Ebola, antibiotic-resistant superbugs, and more. David Blumenthal, STAT, 23 May 2021 But the end of this piece clarifies the meaning of this coronavirus potentially joining the ranks of influenza viruses. Robin Lloyd, Scientific American, 19 Mar. 2021 In the case of influenza A, the genome is broken into eight separate segments. William A. Haseltine, Forbes, 12 Aug. 2022 Dog adoptions have been temporarily halted at the Greater Birmingham Humane Society as part of the organization’s effort to contain a canine influenza outbreak in the area. Howard Koplowitz | Hkoplowitz@al.com, al, 26 July 2022 See More 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
Kids Definition
influenza
noun
in·flu·en·za ˌin-flü-ˈen-zə
: a very contagious virus disease like a severe cold with fever
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."