During a freelance proofing job recently, I came across the following sentence in a caption: "To zest an orange, remove only the thin outer layer of skin, without the white pithy underlayer, using a sharp paring knife, vegetable peeler or zester, and mince."
I chuckled at the use of "pithy," which, I learned upon consulting Webster's, wasn't incorrect. In fact, its first definition ("of, like, or full of pith") told me that it was absolutely the correct usage. But I recommended changing it to "pith." Why?
Because when I read "pithy," I was inferring Webster's second definition: "terse and full of substance or meaning." Even though the word was being used correctly, I made the judgment that Webster's second definition was what would come to readers' minds, which would probably lead them to chuckle much as I did (well, not exactly. I mean, I have a pretty distinctive chuckle -- think Ed Grimley).
My point? Copy editing isn't always about rigid rules. Sometimes you have to go on feel, like the way Jim Leyland puts together a lineup. If a construction hits you as peculiar, you've gotta change it.
And, if you're wondering, it does not bug me that I changed an adjective to a noun. I think it still works. So there.