Apparently this seems to be an ongoing and contentious internet debate lol. There's even a wiki article on the subject.[1] The main three arguments appear to be

Apparently this seems to be an ongoing and contentious internet debate lol. There's even a wiki article on the subject.[1] The main three arguments appear to be that virii 1) is grammatically incorrect Latin, 2) virus has historically never had a latin plural "as it is a mass noun" and 3) it's a neologistic folk etymology. While I may agree with the grammatical merits [1)] I'm not convinced (yet). The second argument [2)] that it's never had a historical plural doesn't hold up. The field of virology is much more recent so the need for a plural 'virus' didn't exist at the time. And 3) is literally how words are formed. If a term used frequently enough it eventually becomes a word regardless of the original grammatical correctness. The term even has 175 years of precedent.[2] As cactus has the plural cacti it's non-obvious why the same doesn't hold true for virus. [1] https://en.wikipedia.org/wiki/Plural_form_of_words_ending_in_-us https://en.wikipedia.org/wiki/Plural_form_of_words_ending_in... [2] https://archive.org/details/homopathictreati00test/page/48/mode/2up https://archive.org/details/homopathictreati00test/page/48/m...