"Virii" is wrong. If it were a thing, it would be the plural of "virius", which isn't a word. "The Latin word "virus" isn't widely attested, and never in the p

"Virii" is wrong. If it were a thing, it would be the plural of "virius", which isn't a word. "The Latin word "virus" isn't widely attested, and never in the plural. It seems to refer to something like a miasma - that is, a substance, that has no plural. The English word Virus, refering to a particle of an infectious agent, should therefore be treated as an English word, of which the plural form is "viruses". [Edit] There are singular nouns in Latin that end in "-us", which do have a plural form, but that plural form is spelled the same as the singular form. So it's possible that the plural of the Latin "virus" was "virus". But as far as I'm aware, it wasn't a countable noun. Also, if we want "virus" to mean a particle, then it's inconvenient for the plural to also be "virus" - we'd like a notation for referring to multiple particles. [Edit 2] It's worse, isn't it? We refer to the "Covid-19 virus", meaning the global population of that group of strains; the individual strains in the group might then also be referred to as a singular "virus", in the sense in which we might refer to urban air-pollution being caused by "the car". I gave up using words like "stadia" and "referenda" many years ago. I'm afraid I'm very pedantic about language, but I now think those are a sort of back-Latin, and they sound pretentious. "Stadium" and "referendum" are English words now, and the way normal people pluralise them is correct.