"Virtuous circle"

[No Name Available]

I don't intend to nitpick, either, but this is not the first time I've
encountered the verb, "nitpick," used as adjective, as in "nitpicky." Is this
usage geographically determined, or has it been validated via some legitimate
source?  The first time I heard a speaker use it (around 1989), another
listener "corrected" her (This interplay occurred several times.)  What's the
word on this issue?
                    PAT