Plural of Virus

What Is the Plural of Virus?

The Quick Answer

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.