The plural is viri in Latin but viruses in English. I have seen it as viri in medical journals, but not anywhere else that I recall.

I suspect the reason for this apparent discrepancy is that viruses trips off the tongue better than do radiuses and hippopotamuses. The accented syllable (vir) is too close to the -i to be sonorous (at least in English).

Along those lines, most dictionaries show octopuses or octopi as the plural of octopus. In my view the latter is incorrect since octopus is not from Latin, but from Greek okto (eight) plus pous (foot).




TEd