Is the plural of virus "viruses" or "virii"?
locked by Andrew Leach♦ Oct 18 '16 at 8:36
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Wikipedia has a rather large section dedicated to this question. The verdict is: “The English plural of virus is viruses, not viri.” Merriam-Webster agrees, as does TheFreeDictionary. Wiktionary offers the following usage notes:
The plural is often believed to be viri or even virii, but neither is correct Latin and both are neologistic folk etymology. The word has no plural in Latin as it is a mass noun, like oxygen or sunlight.
Speaking as a descriptivist, I would have to say that "virii" does indeed exist, in English rather than bad Latin, but only as a whimsical or jocular form (and particularly in an IT context). Strictly "viruses" for an unmarked usage.