You’re just nasty
Nuh uh.
We await with bated breath Q.E.D.'s Damascene conversion from persecuting the English language.
And yet, after reading that I’m almost willing to accept penii, just the hypthetical *peni-, -us, -i root to play with. Sort of as the backwards inverse of “genius”, maybe.
“You, sir, are a penius!” “This discussion is sheer penius”
A few interesting points below for y’all.
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Octopus is a Latin word. Latin, like every other language on the planet, sometimes got its words from other languages. And there are two acceptable plurals for it. See link.
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The singular of alumni is alumnus. Those are for the masculine. The feminine singular and plural are: alumna and alumnae. See link.
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There are two acceptable plurals for penis: penises and penes. See link.
That’s certainly news to me. It doesn’t appear in Lewis & Short. Care to provide me with a cite?
Your cite actually says it is Greek, by the way.
I’ll go back on my statement a smidge - I’m sure it was Latinized in the Renaissance in biological texts. That doesn’t actually change anything - ‘octopus’ would not have been pluralized in those texts as ‘octopi’ but instead ‘octopodes’, as I said.
My favourite is omnibi, the plural of omnibus.
And, because I haven’t posted enough in this thread yet (can you blame me? How often do pit threads come up which involve both Latin AND Greek?), I found this as one of the first hits on a google search of ‘octopus’ and ‘Latin’.
Of course it was. I was yanking your chain right back atcha. You big goof, you.
:smack:
Well, thanks for the reassurance, anyway. 
My cite, which you asked me to provide you after I already had, btw, says that it came into English via New Latin from Greek. Thus, it’s (a) a Greek word, (b) a Latin word, and (c) an English word.
Oops. That Helen asked me to provide. :smack:
And to back this up, I refer everyone to AskOxford
When come back, bring octopi.
Yes, I acknowledged that, Monty. That doesn’t mean that it was pluralized, even in Latin, as ‘octopi’. I’m working on finding some ‘New Latin’ instances. In the meanwhile, the OED:
"Plural octopuses, octopi, (rare) octopodes Brit. /ktpdiz/, /ktpdiz/, U.S. /ktopdiz/, /ktpdiz/. [< scientific Latin octopus (1758 or earlier in Linnaeus) < ancient Greek -, (also -, ) eight-footed, an eight-footed creature < - OCTO- + -, foot (see -POD).
The plural form octopodes reflects the Greek plural; cf. OCTOPOD n. The more frequent plural form octopi arises from apprehension of the final -us of the word as the grammatical ending of Latin second declension nouns; this apprehension is also reflected in compounds in octop-: see e.g. OCTOPEAN a., OCTOPIC a., OCTOPINE a., etc.] "
Sorry, forgot to mention this. Since, according the to OED, the first instance of ‘octopus’ in Latin is as late as 1758, they could well have started the error upon its first adoption into Latin, although I still doubt it.
Threads like this one make me want to stick with Pulpo a la Gallega…
My point is that the word itself came into English from Latin, one of the plural endings came into English from Latin, and that although in Latin that’s the wrong plural ending, it’s one of the accepted–and thus correct–pluralizations in English for the word.