Plural of Virus

The Quick Answer

The plural of virus is viruses.

The Plural of Virus

The plural of virus is viruses.

Viruses are found in almost every ecosystem on Earth.
Viruses are considered by some to be a life form, because they carry genetic material and can reproduce.

The noun virus has a Latin root, but is one of the few nouns that has no plural in Latin. It occurs only in the singular. The English plural viruses (which adheres to the standard rules for forming plurals) is the only way to make the noun virus plural.

The noun virus adheres to the standard rules for forming the plurals of nouns in English (shown in the table below).

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The Standard Rules for Forming the Plurals

The table below shows the standard rules for forming the plurals of nouns in English.

Type	Example of Type	Forming the Plural	Plural
Most Nouns	lamp scythe	add s	lamps scythes
Noun Ending s, sh, ch, x or z	virus dress	add es	viruses dresses
Nouns ending [consonant] o	hero zero tomato	add either s or es (There are no rules for this - you have to know.)	heroes zeros tomatoes
Nouns ending [vowel] o	patio ratio	add s	patios ratios
Nouns ending [consonant] y	story penny	change the y to an i and add es	stories pennies
Nouns ending [vowel] y	donkey chimney	add s	donkeys chimneys
Nouns ending f or fe	dwarf hoof	ves and/or s (There are no rules - you have to know.)	dwarfs hooves or hoofs
Exceptions	man louse	some nouns undergo a vowel or letters change	men lice
More exceptions	salmon sheep	some nouns do not change at all	salmon sheep
Foreign rulings	fungus medium	some nouns adopt foreign rulings	fungi media

Why Is There Confusion over the Plural of Virus?

Viruses is the only way to make the noun virus plural.

Confusion arises over the plural of virus because people mistakenly believe that viri or virii is its Latin plural form, (in the same way that fungus, cactus, and hippopotamus become fungi, cacti, and hippopotami). Virus is one of the few Latin nouns without a Latin plural.

Another Interactive Exercise

Here are three randomly selected questions from another exercise on plurals, which can be edited, printed to create an exercise worksheet, or sent via email to friends or students.

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