While the french equivalent "pénultième" is rarely heard and considered as pedantic, "antépénultième" is actually much more frequently used to avoid the ugly "avant-avant-dernier" (very really awesome).
It seemed somewhat plausible or serious to me because "ultimate" is slang for "really cool" in India. (At least it was when I was growing up; who knows what the cool kids there say these days.) But I was puzzled because I've spent the majority of my adult life in North America, and never heard "penultimate" used that way.
I was wrong. Apparently it is slang, in some places at least:
> The word penultimate as a slang word seems to have worked its way into common parlance thanks to the slang use of the word ultimate. As a slang term, ultimate means cool rather than last. So the hipster logic may have concluded that if ultimate means cool, then penultimate must mean super cool.
I think it's used in marketing sometimes because it sounds cool, so you'll assume it means something good if you don't understand it. Doesn't come up a lot though.
I shouldn't start on these but I fail to resist, since you bring one of them on the discussion.
This is one of numerous "faux-amis" that are so tricky for native French speakers. While "fameux" has the meaning an English speaker would expect, "Infâme" means odious. Other examples include "éventuellement" that means possibly (and not surely in the future), "actuellement" which translates as "nowadays" (and not really) etc.
It may be chauvinism, but etymological and geographical clues let be believe that most of these are french words that have been imported into English and whose meanings changed radically. Admittedly, some probably share a common latin origin and were declined into similar words but retaining a different subset of their original meanings.
It is often a source of weird misunderstandings between native French and English speakers, neither of which are famous for their mastery at learning foreign languages...