Secretive; reserved is what Wiktionary lists for private in this case. Generally, in my idiolect, it's not really secretive. It's more just reserved.
So would "Is priobhaideach e an buachaill" be "The boy is private"? (if you added the fadas as well, obviously!)
"Is...é" is typically only used for connecting nouns, like "he is a boy." "The boy is private" would be "tá an buachaill priobhaideach."
Why is "priobhaideach" pronounced like "pree-vuh-dach"? I thought 'bh' was pronounced like 'w' when it was around an 'a', 'o', or 'u'.....
The usual answer to this question is dialect - bh is more likely to be "v" in Munster.
The key point, though, is that there isn't really any confusion in meaning - it's not as if either of the pronunciations sounds like some other words.