Humanities › History & Culture The Plural of Virus Share Flipboard Email Print Daniel Sambraus / Getty Images History & Culture Ancient History and Culture Ancient Languages Figures & Events Greece Egypt Asia Rome Mythology & Religion American History African American History African History Asian History European History Genealogy Inventions Latin American History Medieval & Renaissance History Military History The 20th Century Women's History View More By N.S. Gill Ancient History and Latin Expert M.A., Linguistics, University of Minnesota B.A., Latin, University of Minnesota N.S. Gill is a Latinist, writer, and teacher of ancient history and Latin. She has been featured by NPR and National Geographic for her ancient history expertise. our editorial process N.S. Gill Updated August 18, 2018 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 an alumnus. Is the plural of virus viri and if not, why? Neuter and Masculine Nouns Latin neuters end in "-a" in the plural for the nominative and accusative cases: Datum > DataSingular > Plural The plural of virus is viruses in English—at least at the moment. The 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 of 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 the 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 > AlumniSingular > 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. The Flexibility of Language Although viruses are probably the best plural for the virus, while viri are 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. The Plural of 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.