Just out of curiosity, how many grammar rules did you just break? And yet, you conveyed your meaning just fine. Gosh. Who’da thunk it?
The thing about the language purist arguments is that you are already using one hell of a corrupted language. You’re clinging like mad to something so silly, when bigger battles have already been lost. Unshift your vowels! Fight the power!
Mr Greywolf - who, incidentally, uses spellings like “powerfull” and “beleave” - his own bad self!
Fess up, LHOD: you can’t provide any credible cites for “pegasi” - despite your claims that there are too many out there for you to waste your time finding and I wouldn’t like them anyway - because it’s a bullshit word. I, on the other hand, provided a credible and relatively recent cite for “octopods” - from a well-known and respected author - at the beginning of this thread.
Right . . .
First: The fact that the Greeks would have pluralized “octopus” differently is irrelevant; this isn’t a word that is newly coined into English from Greek where no commonly used pluralization already exists.
Second: It is probably incorrect to say “octopi;” if one was to try and set a “rule” for a proper pluralization based upon usage, I’d bet it more likely you would hear “octopuses.” Certainly, kids in a classroom will try that first, and most adults I think will do the same.
Third: If, for sake of argument, most adults in America would use “octopi,” then one would have to give serious consideration to calling that the “proper” pluralization in American English. If someone wants to swim upstream on that, that’s up to him/her, but it just makes you look foolish, Case Sensitive. Of course, I’ve enjoyed looking foolish on similar issues before. 
And I provided cites to a 106 year old Dictionary and you tried to dismiss that. I proved one of your examples of a possible pluralization was in fact the family name and yet you have reduce your logic and argument to making fun of a straw-man that no one else but you supplied. A weak argument indeed.
Pegasi is found throughout modern fantasy novels and games. You can not care for the Genre, but it is not logical or reasonable to dismiss its existence. You are correct that Pegasi has enter semi-popular culture via D&D as so much of modern fantasy is written by authors who cut their teeth in Fantasy on D&D or D&D based novels. Do you dismiss all words that enter the language from “Low-brow” sources?
Jim
“Æthiopia produces the lynx in abundance, and the sphinx, which has brown hair and two mammæ on the breast, as well as many monstrous kinds of a similar nature; horses with wings, and armed with horns, which are called pegasi”
-Pliny the Elder, Natural History (link)
Now, granted Pliny was writing in Latin, but this is an English translation, which uses ‘pegasi’ as a plural form of pegasus for a winged (and horned!) horse. The footnote regarding this part of the passage repeatedly uses ‘pegasus’ as a common noun for winged horses.
Must refrain from saying “Ooh Burn!!”
Pliny the Elder should Trump the little known George MacDonald Fraser, who by the way as a screen writer could be dismissed as a fluff writer.
Jim the juvenile
I dunno. Natural History looks pretty fluffy to me. Manticores, basilisks, cameleopards, dragons, pegasi…it’s like a veritable D&D monster manual. 
Well, okay cameleopards are real - “There are two others animals, which have some resemblance to the camel. One of these is called, by the Æthiopians, the nabun. It has a neck like that of the horse, feet and legs like those of the ox, a head like that of the camel, and is covered with white spots upon a red ground; from which peculiarities it has been called the cameleopard. It was first seen at Rome in the Circensian games held by Cæsar, the Dictator. Since that time too, it has been occasionally seen. It is more remarkable for the singularity of its appearance than for its fierceness; for which reason it has obtained the name of the wild sheep.” - if you’re still having trouble, he’s talking about giraffes.
What’s the plural of “booyah!”?
Case Sensitive, your entire argument boils down to a sneer. When discussing the differently girlfriend-enabled, I wonder about someone who thinks that their pluralization of octopus makes them superior to others, and about their poor dates.
Daniel
OK, now that’s a cite. I don’t much like the word, but pegasi it is. However, I still maintain that “octopi” is and always will be wrong.
Oh, and Excalibre? Podunk!
My apologies to Mr Greywolf, too.
I am very happy you accept Pliny. Somehow that is one of the funniest and most definite cites I have ever seen.
You have seen many arguments and a few cites for Octopi.
My wife suggests that the proper Plural of Octopus may well be Octopus.
It appears that the 1911 Encyclopedia Britannica used that form.
Anyone else in possession of old encyclopedias or dictionaries.
I checked some Popular Sciences from the 1870’s I have but no help there. No index hit on Octopus.
sinjin found and posted that the OED uses Octopi.
I’ll add this one: 1913 Webster’s New International Dictionary
Page 1489:
So no Greek version is acceptable in English. At some point you might want to admit that while you are right in your heart, you are wrong in English.
Your argument is based on the: The word is Greek, so we should use the Greek rules. It seems apparent that several authorities on the English language disagree with you.
Jim
Just to add to the confusion, The 1938 Encyclopedia Britannica on page 700 of volume 16 is using **Octopods ** as the apparent plural of Octopus in the article that is a slight rewrite of the online 1911 one I linked to earlier.
So I have found a cite to back you up Case Sensitive.
Anyone notice I have way too many very old reference books in my house?
Jim
Webster’s New Twentieth Century Unabridged Dictionary. 1983. Page 1239
Scott, Foresman Advanced Dictionary, Doubleday Edition. 1979. Page 709-710
Provides no plurals but has an entry to that
The Online Etymology Dictionary: I plan to Email them this thread for review of their entry.
Yeah. I’ve explained why the plural of “appendix” is “appendices” to lots of people, and I’ve never gotten a date out of it. I’m not sure Case Sensitive’s logic about girlfriends really applies.
Actually, the OED says that the plural of octopus is octopodes but (as of the most recent addition) they have conceded that octopi is more common. However, they do so with that lovely British philological disdain. To requote:
When I read this, I see a spindly old man in a shawl shuddering at the very thought of those barbarians who would say octopi.
OK, so while reading this exercise in arcane stuff, a couple of our teen members, afflicted with acne, were moved to pick at their pimples, and of course between them they squeezed out pi.
Would you rather they squeeze out podes?
Daniel
Can I mention that octopi annoys the fuck out of me? I’d like to personally give a bloody nose to everybody who goes around inventing fake Latin plurals for words. Except when they’re joking. Lord help me, I’ve seen people here on the SDMB use penii instead of penises or penes. Where the hell did this notion of plurals in -ii come from in the first place?
If there were fewer people who got irritated over nonstandard plurals, there would probably be fewer people who made Latinerrific plurals out of nonLatinaceous words. It’s the folks who insist on “antennae” and “succubi” who are responsible for “pegasi” and “penii”: folks who haven’t studied Latin know that these podesantic will sneer at them if they form improper plurals, and so they do their best to avoid those sneers.
Daniel