What Is the Plural of Virus?

Question: What Is the Plural of Virus?

It is common knowledge that the plurals of many words from Latin end in "-a" or "-i". Data, for instance, is the plural of datum and alumni is the plural of alumnus. Is the plural of virus viri and if not, why?

Answer:

Latin neuters end in "-a" in the plural for the nominative and accusative cases.
Datum > Data
Singular > Plural

The plural of virus is viruses in English -- at least at the moment. Virus is a neuter noun in Latin. That means its plural, if there were an attested ancient usage of virus in the plural, would have ended in an "-a," because neuter nouns in (ancient Greek and) Latin end in an "-a," in the plural nominative and accusative cases. The example of the plural of datum is a case in point. Since datum is a neuter singular, its plural is data.

Since virus is neuter, vira is a possibility for the nominative/accusative plural. It could not be viri.

Second declension masculine nouns end in "-i" in the nominative plural.
Alumnus > Alumni
Singular > Plural

Viri is the plural of the masculine 2nd declension noun vir, which means 'man'. Vir 'man' is a masculine noun and the "-i" ending is appropriate for the plural nominative of masculine second declension nouns.

However...

Although viruses is probably the best plural for virus, while viri is currently wrong, languages change. Because of the frequency with which viruses threaten the Internet, and the resultant frequency of articles using various endings on the word virus, we may have a new standard plural for virus before we know it.

A Related Note: Octopus

Octopus comes from the Greek, so the -us ending does not mark a Latin masculine noun of the second declension. The Greek-based plural is octopodes, but like other words taken into English, an -es ending on the singular (octopus > octopuses) is acceptable. Octopi is wrong for the plural of octopus, like viri for the plural of virus.

Latin FAQ Index

• Is Latin easy?
• What do the Latin tenses mean?
• Do you have any tips on memorizing endings?
• Where can I find a Latin translation of...?
• In Latin, how do you say "I used to go"? "Fearless and determined"? "Thank you"?
• What is the correct Latin for "deus lo vult"?
• What is the plural of virus?
• Why does the neuter nominative and accusative plural match the nominative feminine singular?
• Are our borrowed words from French or Latin?