The plurals of 'Prius'

This morning John heard a WBUR reporter jokingly refer to the plural of the Toyota Prius as "Prii," and he wondered: Could that Latin plural be right, or was this plural form just a misbegotten language hybrid, as it were?

Well, my Latin is minimal and creaky, but Miss Madge Mossman (R.I.P) equipped me with enough grammar for a Google search. And the first thing I found was the much-quoted misinformation provided by a Toyota spokesman back in 2004. "Prius is a Latin word meaning 'to go before,'" he explained. "Toyota chose this name because the Prius vehicle is the predecessor of cars to come."

But prius can't be a Latin infinitive; "to go before" would have to be a verb, like, say, precedere. Actually, prius is just the neuter form of prior, the comparative adjective, meaning "earlier, anterior, superior." As a noun, it would mean "earlier one" or "superior one." And its plural would be, if I read aright, not Prii but Prioria.

Pleasant enough -- but as it happens, prioria is also medieval Latin for "priories." And while Prius drivers are a devout lot, they probably don't think of their cars as nunneries and monasteries. I'm guessing we'll settle down with the standard English plural; after all, we've got plenty of words weirder than Priuses.