I'm not about to smash you over the head with a chair, Squid, but you're saying it wrong. Just so you know. Star Trek's Data (day tah) persistently corrected people who called him Data (dah tah), saying he wasn't plural. But you're right, there are more urgent things to worry about than poTAYtoes and poTAHtoes. I'll go back to work now. How about plethora of prii? (pree eye, as in more than one)
'prius' means 'before' in Latin. There is no correct plural because it's not a noun. Prius, as used as the name of a car, would just be pluralized Priuses since it's not a real Latin word, but I admit it is fun to call the plural Prii.
Well, yeah, I call it prye-is ... isn't it based somehow on the English language 'ius' ? So far, noone's looking at me weird - unless I'm in my Driftwood!!! and they're wondering what kind of car it is!
I can't think of a single word with an ending 'ius' that's pronounced "eye-us". Radius is ray-dee-us, for example. Closest I can come up with is pious, but that's a different spelling.
From my limited knowledge of liturgical Latin (choral singer, not priest!), "PREE-oos" would be about right. Latin does not have the English "uh." A slightly rolled "r" makes "PREE-oos' sound even more liturgical. However, neither I nor, probably, anybody else on this group has ever heard the word pronounced this way.
Every time my wife sees a Prius, she calls out "Priapus!" So that's how it's pronounced in my house. The classic Prius is just a Prius, but to her the hatchback will always be Priapus.