Masculine Latin nouns can be equally problematic, though. Who has not wondered about whether to write plural locus as loci (would it be pretentious)? The thing there is that not all words that end in “–us” are of Latin origin, and so not all are pluralized as “–i.” Octopus, for example, is from Greek and so should always be pluralized as octopuses.
And you would never write hiati as a plural for hiatus, or viri as plural for virus. It makes no sense, but that’s English for you. And ignoramus is not a Latin noun at all, but a verb (meaning “we do not know”), so it would make no sense to try to Latinize its plural in English. My dad used to fume about agenda used as a singular – he would insist it’s plural – but even Fowler says to stop worrying about that. The important thing to remember is that we are speaking English, not Latin.
Stamina is even more confusing – in Latin it’s the plural of stamen, a word we now use for a part of a plant. The two words have nothing to do with each other in English now, so don’t worry about it. You wouldn’t count staminas anyway.
(Russel Smith. At the risk of sounding archaic, I still think that media is plural. The Globe and Mail. October 29, 2010.)